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Chapter One
1.1 Introduction to programming
A Computer is an electronic device that accepts data, performs computations, and makes
logical decisions according to instructions that have been given to it; then produces
meaningful information in a form that is useful to the user. In current world we live in,
computers are almost used in all walks of life for different purposes. They have been
deployed to solve different real life problems, from the simplest game playing up to the
complex nuclear energy production. Computers are important and widely used in our
society because they are cost-effective aids to problem solving in business, government,
industry, education, etc.
In order to solve a given problem, computers must be given the correct instruction about
how they can solve it. The terms computer programs, software programs, or just
programs are the instructions that tells the computer what to do. Computer requires
programs to function, and a computer programs does nothing unless its instructions are
executed by a CPU. Computer programming (often shortened to programming or
coding) is the process of writing, testing, debugging/troubleshooting, and maintaining the
source code of computer programs. Writing computer programs means writing
instructions that will make the computer follow and run a program based on those
instructions. Each instruction is relatively simple, yet because of the computer's speed, it
is able to run millions of instructions in a second. A computer program usually consists of
two elements:
 Data – characteristics
 Code – action+
A computer program (also known as source code) is often written by professionals
known as Computer Programmers (simply programmers). Source code is written in one
of programming languages.
A programming language is an artificial language that can be used to control the
behavior of a machine, particularly a computer. Programming languages, like natural
language (such as English), are defined by syntactic and semantic rules which describe
their structure and meaning respectively. The syntax of a language describes the possible
combinations of symbols that form a syntactically correct program. The meaning given to
a combination of symbols is handled by semantics. Many programming languages have
some form of written specification of their syntax and semantics; some are defined only
by an official implementation. In general, programming languages allow humans to
communicate instructions to machines.
A main purpose of programming languages is to provide instructions to a computer. As
such, programming languages differ from most other forms of human expression in that
they require a greater degree of precision and completeness. When using a natural
language to communicate with other people, human authors and speakers can be
ambiguous and make small errors, and still expect their intent to be understood. However,
computers do exactly what they are told to do, and cannot understand the code the
programmer "intended" to write. So computers need to be instructed to perform all the
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tasks. The combination of the language definition, the program, and the program's inputs
must fully specify the external behavior that occurs when the program is executed.
Computer languages have relatively few, exactly defined, rules for composition of
programs, and strictly controlled vocabularies in which unknown words must be defined
before they can be used.
Available programming languages come in a variety of forms and types. Thousands of
different programming languages have been developed, used, and discarded.
Programming languages can be divided in to two major categories:
 Low-level languages
 High-level languages.
Low-level languages
Computers only understand one language and that is binary language or the language of
1s and 0s. Binary language is also known as machine language, one of low-level
languages. In the initial years of computer programming, all the instructions were given
in binary form. Although the computer easily understood these programs, it proved too
difficult for a normal human being to remember all the instructions in the form of 0s and
1s. Therefore, computers remained mystery to a common person until other languages
such as assembly language was developed, which were easier to learn and understand.
Assembly language correspondences symbolic instructions and executable machine
codes and was created to use letters (called mnemonics) to each machine language
instructions to make it easier to remember or write. For example:
ADD A, B – adds two numbers in memory location A and B
Assembly language is nothing more than a symbolic representation of machine code,
which allows symbolic designation of memory locations. However, no matter how close
assembly language is to machine code, computers still cannot understand it. The
assembly language must be translated to machine code by a separate program called
assembler. The machine instruction created by the assembler from the original program
(source code) is called object code. Thus assembly languages are unique to a specific
computer (machine). Assemblers are written for each unique machine language.
High-level languages
Although programming in assembly language is not as difficult and error prone as
stringing together ones and zeros, it is slow and cumbersome. In addition it is hardware
specific. The lack of portability between different computers led to the development of
high-level languages—so called because they permitted a programmer to ignore many
low-level details of the computer's hardware. Further, it was recognized that the closer
the syntax, rules, and mnemonics of the programming language could be to "natural
language" the less likely it became that the programmer would inadvertently introduce
errors (called "bugs") into the program. High-level languages are more English-like and,
therefore, make it easier for programmers to "think" in the programming language. Highlevel languages also require translation to machine language before execution. This
translation is accomplished by either a compiler or an interpreter. Compilers translate
the entire source code program before execution. Interpreters translate source code
programs one line at a time. Interpreters are more interactive than compilers. FORTRAN
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(FORmula TRANslator), BASIC (Bingers All Purpose Symbolic Instruction Code),
PASCAL, C, C++, Java are some examples of high-level languages.
The question of which language is best is one that consumes a lot of time and energy
among computer professionals. Every language has its strengths and weaknesses. For
example, FORTRAN is a particularly good language for processing numerical data, but it
does not lend itself very well to organizing large programs. Pascal is very good for
writing well-structured and readable programs, but it is not as flexible as the C
programming language. C++ embodies powerful object-oriented features
As might be expected in a dynamic and evolving field, there is no single standard for
classifying programming languages. Another most fundamental ways programming
languages are characterized (categorized) is by programming paradigm. A programming
paradigm provides the programmer's view of code execution. The most influential
paradigms are examined in the next three sections, in approximate chronological order.
Procedural Programming Languages
Procedural programming specifies a list of operations that the program must complete to
reach the desired state. Each program has a starting state, a list of operations to complete,
and an ending point. This approach is also known as imperative programming. Integral to
the idea of procedural programming is the concept of a procedure call.
Procedures, also known as functions, subroutines, or methods, are small sections of code
that perform a particular function. A procedure is effectively a list of computations to be
carried out. Procedural programming can be compared to unstructured programming,
where all of the code resides in a single large block. By splitting the programmatic tasks
into small pieces, procedural programming allows a section of code to be re-used in the
program without making multiple copies. It also makes it easier for programmers to
understand and maintain program structure.
Two of the most popular procedural programming languages are FORTRAN and BASIC.
Structured Programming Languages
Structured programming is a special type of procedural programming. It provides
additional tools to manage the problems that larger programs were creating. Structured
programming requires that programmers break program structure into small pieces of
code that are easily understood. It also frowns upon the use of global variables and
instead uses variables local to each subroutine. One of the well-known features of
structural programming is that it does not allow the use of the GOTO statement. It is
often associated with a "top-down" approach to design. The top-down approach begins
with an initial overview of the system that contains minimal details about the different
parts. Subsequent design iterations then add increasing detail to the components until the
design is complete.
The most popular structured programming languages include C, Ada, and Pascal.
Object-Oriented Programming Languages
Object-oriented programming is one the newest and most powerful paradigms. In objectoriented programs, the designer specifies both the data structures and the types of
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operations that can be applied to those data structures. This pairing of a piece of data with
the operations that can be performed on it is known as an object. A program thus
becomes a collection of cooperating objects, rather than a list of instructions. Objects can
store state information and interact with other objects, but generally each object has a
distinct, limited role.
1.2 Problem solving Techniques
Computer solves varieties of problems that can be expressed in a finite number of steps
leading to a precisely defined goal by writing different programs. A program is not
needed only to solve a problem but also it should be reliable, (maintainable) portable and
efficient. In computer programming two facts are given more weight:
 The first part focuses on defining the problem and logical procedures to follow in
solving it.
 The second introduces the means by which programmers communicate those
procedures to the computer system so that it can be executed.
There are system analysis and design tools, particularly flowchart and structure chart, that
can be used to define the problem in terms of the steps to its solution. The programmer
uses programming language to communicate the logic of the solution to the computer.
Before a program is written, the programmer must clearly understand what data are to be
used, the desired result, and the procedure to be used to produce the result. The
procedure, or solution, selected is referred to as an algorithm. An algorithm is defined as
a step-by-step sequence of instructions that must terminate and describe how the data is
to be processed to produce the desired outputs. Simply, algorithm is a sequence of
instructions. Algorithms are a fundamental part of computing. There are three commonly
used tools to help to document program logic (the algorithm). These are flowcharts,
structured chart, and Pseudocode. We will use the three methods here. Generally,
flowcharts work well for small problems but Pseudocode is used for larger problems.
1.2.1 Pseudocode
Pseudocode (derived from pseudo and code) is a compact and informal high-level
description of a computer algorithm that uses the structural conventions of programming
languages, but typically omits detailes such as subroutines, variables declarations and
system-specific syntax. The programming language is augmented with natural language
descriptions of the details, where convenient, or with compact mathematical notation.
The purpose of using pseudocode is that it may be easier for humans to read than
conventional programming languages, and that it may be a compact and environmentindependent generic description of the key principles of an algorithm. No standard for
pseudocode syntax exists, as a program in pseudocode is not an executable program. As
the name suggests, pseudocode generally does not actually obey the synatx rules of any
particular language; there is no systematic standard form, although any particular writer
will generally borrow the appearance of a particular language.
The programming process is a complicated one. You must first understand the program
specifications, of course, Then you need to organize your thoughts and create the
program. This is a difficult task when the program is not trivial (i.e. easy). You must
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break the main tasks that must be accomplished into smaller ones in order to be able to
eventually write fully developed code. Writing pseudocode will save you time later
during the construction & testing phase of a program's development.
Example:
Original Program Specification:
Write a program that obtains two integer numbers from the user. It will
print out the sum of those numbers.
Pseudocode:
Prompt the user to enter the first integer
Prompt the user to enter a second integer
Compute the sum of the two user inputs
Display an output prompt that explains the answer as the
sum
Display the result
1.2.2 Structured Charts
Structured chart depicts the logical functions to the solution of the problem using a chart.
It provides an overview that confirms the solution to the problem without excessive
consideration to detail. It is high-level in nature.
Example: Write a program that asks the user to enter a temperature reading in centigrade
and then prints the equivalent Fahrenheit value.
Input
Centigrade
Process
 Prompt for centigrade value
 Read centigrade value
 Compute Fahrenheit value
 Display Fahrenheit value
Output
Fahrenheit
CelsusToFarh
(main func)
centigard
InPutCen
centigard
CalcFar
Fahrenheit
OutPutFar
Fahrenheit
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1.2.3 Flowchart
A flowchart (also spelled flow-chart and flow chart) is a schematic representation of
an algorithm or a process. The advantage of flowchart is it doesn‘t depend on any
particular programming language, so that it can used, to translate an algorithm to more
than one programming language. Flowchart uses different symbols (geometrical shapes)
to represent different processes. The following table shows some of the common
symbols.
Example 1: - Draw flow chart of an algorithm to add two numbers and display their
result.
Algorithm description

Read the rules of the two numbers (A and B)


Add A and B
Assign the sum of A and B to C

Display the result ( c)
The flow chart is:
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Start
Read A, B
C= A+B
Print C
End
Example 2: Write an algorithm description and draw a flow chart to check a number is
negative or not.
Algorithm description.
1/ Read a number x
2/ If x is less than zero write a message negative
else write a message not negative
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Sometimes there are conditions in which it is necessary to execute a group of statements
repeatedly. Until some condition is satisfied. This condition is called a loop. Loop is a
sequence of instructions, which is repeated until some specific condition occurs. A loop
normally consists of four parts. These are:
Initialization: - Setting of variables of the computation to their initial values and setting
the counter for determining to exit from the loop.
Computation: - Processing
Test: - Every loop must have some way of exiting from it or else the program would
endlessly remain in a loop.
Increment: - Re-initialization of the loop for the next loop.
Example 3: - Write the algorithmic description and draw a flow chart to find the
following sum.
Sum = 1+2+3+…. + 50
Algorithmic description
1. Initialize sum too and counter to 1
1.1. If the counter is less than or equal to 50
• Add counter to sum
• Increase counter by 1
• Repeat step 1.1
1.2. Else
• Exit
2. Write sum
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1.3 System Development Life Cycle (SDLC)
The Systems Development Life Cycle (SDLC) is a conceptual model used in project
management that describes the stages involved in a computer system development project
from an initial feasibility study through maintenance of the completed application. The
phases of SDLC are discussed below briefly.
1.3.1 Feasibility study
The first step is to identify a need for the new system. This will include determining
whether a business problem or opportunity exists, conducting a feasibility study to
determine if the proposed solution is cost effective, and developing a project plan.
This process may involve end users who come up with an idea for improving their work
or may only involve IS people. Ideally, the process occurs in tandem with a review of the
organization's strategic plan to ensure that IT is being used to help the organization
achieve its strategic objectives. Management may need to approve concept ideas before
any money is budgeted for its development.
A preliminary analysis, determining the nature and scope of the problems to be solved is
carried out. Possible solutions are proposed, describing the cost and benefits. Finally, a
preliminary plan for decision making is produced.
The process of developing a large information system can be very costly, and the
investigation stage may require a preliminary study called a feasibility study, which
includes e.g. the following components:
a. Organizational Feasibility

How well the proposed system supports the strategic objectives of the
organization.
b. Economic Feasibility
 Cost savings
 Increased revenue
 Decreased investment
 Increased profits
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c. Technical Feasibility

Hardware, software, and network capability, reliability, and availability
d. Operational Feasibility



End user acceptance
Management support
Customer, supplier, and government requirements
1.3.2 Requirements analysis
Requirements analysis is the process of analyzing the information needs of the end users,
the organizational environment, and any system presently being used, developing the
functional requirements of a system that can meet the needs of the users. Also, the
requirements should be recorded in a document, email, user interface storyboard,
executable prototype, or some other form. The requirements documentation should be
referred to throughout the rest of the system development process to ensure the developing
project aligns with user needs and requirements.
End users must be involved in this process to ensure that the new system will function
adequately and meets their needs and expectations.
1.3.3 Designing solution
After the requirements have been determined, the necessary specifications for the
hardware, software, people, and data resources, and the information products that will
satisfy the functional requirements of the proposed system can be determined. The design
will serve as a blueprint for the system and helps detect problems before these errors or
problems are built into the final system.
The created system design, but must reviewed by users to ensure the design meets users'
needs.
1.3.4 Testing designed solution
A smaller test system is sometimes a good idea in order to get a ―proof-of-concept‖
validation prior to committing funds for large scale fielding of a system without knowing if
it really works as intended by the user.
1.3.5 Implementation
The real code is written here. Systems implementation is the construction of the new
system and its delivery into production or day-to-day operation.The key to understanding
the implementation phase is to realize that there is a lot more to be done than programming.
Implementation requires programming, but it also requires database creation and
population, and network installation and testing. You also need to make sure the people are
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taken care of with effective training and documentation. Finally, if you expect your
development skills to improve over time, you need to conduct a review of the lessons
learned.
1.3.6 Unit testing
Normally programs are written as a series of individual modules, these subject to separate
and detailed test.
1.3.7 Integration and System testing
Bring all the pieces together into a special testing environment, then checks for errors, bugs
and interoperability. The system is tested to ensure that interfaces between modules work
(integration testing), the system works on the intended platform and with the expected
volume of data (volume testing) and that the system does what the user requires
(acceptance/beta testing).
1.3.8 Maintenance
What happens during the rest of the software's life: changes, correction, additions, moves to
a different computing platform and more. This, the least glamorous and perhaps most
important step of all, goes on seemingly forever.
Chapter Two
C++ Basics
2.1. Structure of C++ Program
A C++ program has the following structure
[Comments]
[Preprocessor directives]
[Global variable declarations]
[Prototypes of functions]
[Definitions of functions]
2.2. C++ IDE
The complete development cycle in C++ is: Write the program, compile the source code,
link the program, and run it.
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Writing a Program
To write a source code, your compiler may have its own built-in text editor, or you may be
using a commercial text editor or word processor that can produce text files. The important
thing is that whatever you write your program in, it must save simple, plain-text files, with
no word processing commands embedded in the text. Examples of safe editors include
Windows Notepad, the DOS Edit command, EMACS, and VI (for Linux). Many
commercial word processors, such as WordPerfect, Word, and dozens of others, also offer
a method for saving simple text files.
The files you create with your editor are called source files, and for C++ they typically are
named with the extension .CPP
Compiling
Your source code file can't be executed, or run, as a program can. To turn your source code
into a program, you use a compiler. How you invoke your compiler, and how you tell it
where to find your source code, will vary from compiler to compiler; check your
documentation. In Borland's Turbo C++ you pick the RUN menu command or type
tc <filename>
from the command line, where <filename> is the name of your source code file (for
example, test.cpp). Other compilers may do things slightly differently. After your source
code is compiled, an object file is produced. This file is often named with the extension
.OBJ.
This is still not an executable program, however. To turn this into an executable
program, you must run your linker.
Linking
C++ programs are typically created by linking together one or more OBJ files with one or
more libraries. A library is a collection of linkable files that were supplied with your
compiler, that you purchased separately, or that you created and compiled. All C++
compilers come with a library of useful functions (or procedures) and classes that you can
include in your program. A function is a block of code that performs a service, such as
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adding two numbers or printing to the screen. A class is a collection of data and related
functions.
Summary
The steps to create an executable file are
1. Create a source code file, with a .CPP extension.
2. Compile the source code into a file with the .OBJ extension.
3. Link your OBJ file with any needed libraries to produce an executable program.
2.3. Showing Sample program
Any meaningful program written in C++ has to contain a number of components: the main
function; some variable declarations; and some executable statements. For example, the
following is a very basic C++ program:
1: #include <iostream.h>
2:
3: int main()
4: {
5: cout << "Hello World!\n";
6:
return 0;
7: }
On line 1, the file iostream.h is included in the file. The first character is the # symbol,
which is a signal to the preprocessor. Each time you start your compiler, the preprocessor is
run. The preprocessor reads through your source code, looking for lines that begin with the
pound symbol (#), and acts on those lines before the compiler runs.
include is a preprocessor instruction that says, "What follows is a filename. Find that file
and read it in right here." The angle brackets around the filename tell the preprocessor to
look in all the usual places for this file. If your compiler is set up correctly, the angle
brackets will cause the preprocessor to look for the file iostream.h in the directory that
holds all the H files for your compiler. The file iostream.h (Input-Output-Stream) is used
by cout, which assists with writing to the screen. The effect of line 1 is to include the file
iostream.h into this program as if you had typed it in yourself.
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The preprocessor runs before your compiler each time the compiler is invoked. The
preprocessor translates any line that begins with a pound symbol (#) into a special
command, getting your code file ready for the compiler.
Line 3 begins the actual program with a function named main(). Every C++ program has a
main() function. In general, a function is a block of code that performs one or more actions.
Usually functions are invoked or called by other functions, but main() is special. When
your program starts, main() is called automatically.
main(), like all functions, must state what kind of value it will return. The return value type
for main() in HELLO.CPP is int, which means that this function will return an integer
value.
All functions begin with an opening brace ({) and end with a closing brace (}). The braces
for the main() function are on lines 4 and 7. Everything between the opening and closing
braces is considered a part of the function.
The meat and potatoes of this program is on line 5. The object cout is used to print a
message to the screen. cout is used in C++ to print strings and values to the screen. A string
is just a set of characters.
Here's how cout is used: type the word cout, followed by the output redirection operator
(<<). Whatever follows the output redirection operator is written to the screen. If you want
a string of characters written, be sure to enclose them in double quotes ("), as shown on line
5. A text string is a series of printable characters.
The final two characters, \n, tell cout to put a new line after the words Hello World! All
ANSI-compliant programs declare main() to return an int. This value is "returned" to the
operating system when your program completes. Some programmers signal an error by
returning the value 1.
The main() function ends on line 7 with the closing brace.
2.4. Basic Elements
2.4.1. Keywords (reserved words)
Reserved/Key words have a unique meaning within a C++ program. These symbols, the
reserved words, must not be used for any other purposes. All reserved words are in lowercase letters. The following are some of the reserved words of C++.
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Asm
const_cast
dynamic_cast
Explicit
Goto
namespace
reinterpret_cast
static_cast
Throw
Union
wchar_t
Fundamental of Programming - I
auto
class
do
extern
if
new
register
static
true
unsigned
Bool
Const
Double
False
Inline
Operator
Return
struct
Try
Using
break
char
delete
float
int
private
short
switch
typedef
virtual
case
continue
else
for
long
protected
signed
template
typeid
void
catch
default
enum
friend
mutable
public
sizeof
this
typename
volatile
Notice that main is not a reserved word. However, this is a fairly technical distinction, and
for practical purposes you are advised to treat main, cin, and cout as if they were reserved
as well.
2.4.2. Identifiers
An identifier is name associated with a function or data object and used to refer to that
function or data object. An identifier must:

Start with a letter or underscore

Consist only of letters, the digits 0-9, or the underscore symbol _

Not be a reserved word
Letter
Syntax of an identifier
Letter
_
Digit
-
For the purposes of C++ identifiers, the underscore symbol, _, is considered to be a letter.
Its use as the first character in an identifier is not recommended though, because many
library functions in C++ use such identifiers. Similarly, the use of two consecutive
underscore symbols, _ _, is forbidden.
The following are valid identifiers
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Length
days_in_year
DataSet1
Int
_Pressure
first_one
A l t ho ug h us i n g _ Pre s su r e i s n ot r e c omm e nd e d .
Profit95
first_1
The following are invalid:
days-in-year
throw
1data
No##
int
bestWish!
first.val
Although it may be easier to type a program consisting of single character identifiers,
modifying or correcting the program becomes more and more difficult. The minor typing
effort of using meaningful identifiers will repay itself many fold in the avoidance of simple
programming errors when the program is modified.
At this stage it is worth noting that C++ is case-sensitive. That is lower-case letters are
treated as distinct from upper-case letters. Thus the word NUM different from the word
num or the word Num. Identifiers can be used to identify variable or constants or functions.
Function identifier is an identifier that is used to name a function.
2.4.3. Literals
Literals are constant values which can be a number, a character of a string. For example the
number 129.005, the character ‗A‘ and the string ―hello world‖ are all literals. There is no
identifier that identifies them.
2.4.4. Comments
A comment is a piece of descriptive text which explains some aspect of a program.
Program comments are totally ignored by the compiler and are only intended for human
readers. C++ provides two types of comment delimiters:

Anything after // (until the end of the line on which it appears) is considered a
comment.

Anything enclosed by the pair /* and */ is considered a comment.
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2.5. Data Types, Variables, and Constants
2.5.1. Variables
A variable is a symbolic name for a memory location in which data can be stored and
subsequently recalled. Variables are used for holding data values so that they can be
utilized in various computations in a program. All variables have two important attributes:

A type, which is, established when the variable is defined (e.g., integer, float,
character). Once defined, the type of a C++ variable cannot be changed.

A value, which can be changed by assigning a new value to the variable. The kind
of values a variable can assume depends on its type. For example, an integer
variable can only take integer values (e.g., 2, 100, -12) not real numbers like 0.123.
Variable Declaration
Declaring a variable means defining (creating) a variable. You create or define a variable
by stating its type, followed by one or more spaces, followed by the variable name and a
semicolon. The variable name can be virtually any combination of letters, but cannot
contain spaces and the first character must be a letter or an underscore. Variable names
cannot also be the same as keywords used by C++. Legal variable names include x,
J23qrsnf, and myAge. Good variable names tell you what the variables are for; using good
names makes it easier to understand the flow of your program. The following statement
defines an integer variable called myAge:
int myAge;
IMPORTANT- Variables must be declared before used!
As a general programming practice, avoid such horrific names as J23qrsnf, and restrict
single-letter variable names (such as x or i) to variables that are used only very briefly. Try
to use expressive names such as myAge or howMany.
A point worth mentioning again here is that C++ is case-sensitive. In other words,
uppercase and lowercase letters are considered to be different. A variable named age is
different from Age, which is different from AGE.
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Creating More Than One Variable at a Time
You can create more than one variable of the same type in one statement by writing the
type and then the variable names, separated by commas. For example:
int myAge, myWeight; // two int variables
long area, width, length; // three longs
As you can see, myAge and myWeight are each declared as integer variables. The second
line declares three individual long variables named area, width, and length. However keep
in mind that you cannot mix types in one definition statement.
Assigning Values to Your Variables
You assign a value to a variable by using the assignment operator (=). Thus, you would
assign 5 to Width by writing
int Width;
Width = 5;
You can combine these steps and initialize Width when you define it by writing
int Width = 5;
Initialization looks very much like assignment, and with integer variables, the difference is
minor. The essential difference is that initialization takes place at the moment you create
the variable.
Just as you can define more than one variable at a time, you can initialize more than one
variable at creation. For example:
// create two int variables and initialize them
int width = 5, length = 7;
This example initializes the integer variable width to the value 5 and the length variable to
the value 7. It is possible to even mix definitions and initializations:
int myAge = 39, yourAge, hisAge = 40;
This example creates three type int variables, and it initializes the first and third.
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2.5.2. Basic Data Types
When you define a variable in C++, you must tell the compiler what kind of variable it is:
an integer, a character, and so forth. This information tells the compiler how much room to
set aside and what kind of value you want to store in your variable.
Several data types are built into C++. The varieties of data types allow programmers to
select the type appropriate to the needs of the applications being developed. The data types
supported by C++ can be classified as basic (fundamental) data types, user defined data
types, derived data types and empty data types. However, the discussion here will focus
only on the basic data types.
Basic (fundamental) data types in C++ can be conveniently divided into numeric and
character types. Numeric variables can further be divided into integer variables and
floating-point variables. Integer variables will hold only integers whereas floating number
variables can accommodate real numbers.
Both the numeric data types offer modifiers that are used to vary the nature of the data to
be stored. The modifiers used can be short, long, signed and unsigned.
The data types used in C++ programs are described in Table 1.1. This table shows the
variable type, how much room it takes in memory, and what kinds of values can be stored
in these variables. The values that can be stored are determined by the size of the variable
types.
Type
Size
unsigned short int
short int(signed short int)
unsigned long int
long int(signed long int)
int
unsigned int
signed int
Char
Float
Double
long double
2 bytes
2 bytes
4 bytes
4 bytes
2 bytes
2 bytes
2 bytes
1 byte
4 bytes
8 bytes
10 bytes
Values
0 to 65,535
-32,768 to 32,767
0 to 4,294,967,295
-2,147,483,648 to 2,147,483,647
-32,768 to 32,767
0 to 65,535
-32,768 to 32,767
256 character values
3.4e-38 to 3.4e38
1.7e-308 to 1.7e308
1.2e-4932 to 1.2e4932
Table C++ data types and their ranges
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2.5.3. Signed and Unsigned
As shown above, integer types come in two varieties: signed and unsigned. The idea here is
that sometimes you need negative numbers, and sometimes you don't. Integers (short and
long) without the word "unsigned" are assumed to be signed. signed integers are either
negative or positive. Unsigned integers are always positive.
Because you have the same number of bytes for both signed and unsigned integers, the
largest number you can store in an unsigned integer is twice as big as the largest positive
number you can store in a signed integer. An unsigned short integer can handle numbers
from 0 to 65,535. Half the numbers represented by a signed short are negative, thus a
signed short can only represent numbers from -32,768 to 32,767.
Example: A demonstration of the use of variables.
2: #include <iostream.h>
3:
4: int main()
5: {
6:
unsigned short int Width = 5, Length;
7:
Length = 10;
8:
9:
10:
11:
// create an unsigned short and initialize with result
// of multiplying Width by Length
unsigned short int Area = Width * Length;
12:
13:
cout << "Width:" << Width << "\n";
14:
cout << "Length: " << Length << endl;
15:
cout << "Area: " << Area << endl;
16:
return 0;
17: }
Output: Width:5
Length: 10
Area: 50
Line 2 includes the required include statement for the iostream's library so that cout will
work. Line 4 begins the program.
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On line 6, Width is defined as an unsigned short integer, and its value is initialized to 5.
Another unsigned short integer, Length, is also defined, but it is not initialized. On line 7,
the value 10 is assigned to Length.
On line 11, an unsigned short integer, Area, is defined, and it is initialized with the value
obtained by multiplying Width times Length. On lines 13-15, the values of the variables are
printed to the screen. Note that the special word endl creates a new line.
Wrapping around integer values
The fact that unsigned long integers have a limit to the values they can hold is only rarely a
problem, but what happens if you do run out of room? When an unsigned integer reaches
its maximum value, it wraps around and starts over, much as a car odometer might. The
following example shows what happens if you try to put too large a value into a short
integer.
Example: A demonstration of putting too large a value in a variable
1: #include <iostream.h>
2: int main()
3: {
4:
unsigned short int smallNumber;
5:
smallNumber = 65535;
6:
cout << "small number:" << smallNumber << endl;
7:
smallNumber++;
8:
cout << "small number:" << smallNumber << endl;
9:
smallNumber++;
10:
cout << "small number:" << smallNumber << endl;
11:
return 0;
12: }
Output: small number:65535
small number:0
small number:1
A signed integer is different from an unsigned integer, in that half of the values you can
represent are negative. Instead of picturing a traditional car odometer, you might picture
one that rotates up for positive numbers and down for negative numbers. One mile from 0
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is either 1 or -1. When you run out of positive numbers, you run right into the largest
negative numbers and then count back down to 0. The whole idea here is putting a number
that is above the range of the variable can create unpredictable problem.
Example: A demonstration of adding too large a number to a signed integer.
1: #include <iostream.h>
2: int main()
3: {
4:
short int smallNumber;
5:
smallNumber = 32767;
6:
cout << "small number:" << smallNumber << endl;
7:
smallNumber++;
8:
cout << "small number:" << smallNumber << endl;
9:
smallNumber++;
10:
cout << "small number:" << smallNumber << endl;
11:
return 0;
12: }
Output: small number:32767
small number:-32768
small number:-32767
IMPORTANT – To any variable, do not assign a value that is beyond its range!
2.5.4. Characters
Character variables (type char) are typically 1 byte, enough to hold 256 values. A char can
be interpreted as a small number (0-255) or as a member of the ASCII set. ASCII stands for
the American Standard Code for Information Interchange. The ASCII character set and its
ISO (International Standards Organization) equivalent are a way to encode all the letters,
numerals, and punctuation marks.
In the ASCII code, the lowercase letter "a" is assigned the value 97. All the lower- and
uppercase letters, all the numerals, and all the punctuation marks are assigned values
between 1 and 128. Another 128 marks and symbols are reserved for use by the computer
maker, although the IBM extended character set has become something of a standard.
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2.5.5. Characters and Numbers
When you put a character, for example, `a', into a char variable, what is really there is just a
number between 0 and 255. The compiler knows, however, how to translate back and forth
between characters (represented by a single quotation mark and then a letter, numeral, or
punctuation mark, followed by a closing single quotation mark) and one of the ASCII
values.
The value/letter relationship is arbitrary; there is no particular reason that the lowercase "a"
is assigned the value 97. As long as everyone (your keyboard, compiler, and screen) agrees,
there is no problem. It is important to realize, however, that there is a big difference
between the value 5 and the character `5'. The latter is actually valued at 53, much as the
letter `a' is valued at 97.
2.6. Operators
C++ provides operators for composing arithmetic, relational, logical, bitwise, and
conditional expressions. It also provides operators which produce useful side-effects, such
as assignment, increment, and decrement. We will look at each category of operators in
turn. We will also discuss the precedence rules which govern the order of operator
evaluation in a multi-operator expression.
2.6.1. Assignment Operators
The assignment operator is used for storing a value at some memory location (typically
denoted by a variable). Its left operand should be an lvalue, and its right operand may be an
arbitrary expression. The latter is evaluated and the outcome is stored in the location
denoted by the lvalue.
An lvalue (standing for left value) is anything that denotes a memory location in which a
value may be stored. The only kind of lvalue we have seen so far is a variable. Other kinds
of lvalues (based on pointers and references) will be described later. The assignment
operator has a number of variants, obtained by combining it with the arithmetic and bitwise
operators.
Operator
=
Example
n = 25
Equivalent To
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+=
-=
*=
/=
%=
&=
|=
^=
<<=
>>=
Fundamental of Programming - I
n += 25
n -= 25
n *= 25
n /= 25
n %= 25
n &= 0xF2F2
n |= 0xF2F2
n ^= 0xF2F2
n <<= 4
n >>= 4
n = n + 25
n = n – 25
n = n * 25
n = n / 25
n = n % 25
n = n & 0xF2F2
n = n | 0xF2F2
n = n ^ 0xF2F2
n = n << 4
n = n >> 4
An assignment operation is itself an expression whose value is the value stored in its left
operand. An assignment operation can therefore be used as the right operand of another
assignment operation. Any number of assignments can be concatenated in this fashion to
form one expression. For example:
int m, n, p;
m = n = p = 100;
m = (n = p = 100) + 2;
// means: n = (m = (p = 100));
// means: m = (n = (p = 100)) + 2;
2.6.2. Arithmetic Operators
C++ provides five basic arithmetic operators. These are summarized in table below
Operator
+
*
/
%
Name
Example
Addition
12 + 4.9
Subtraction
3.98 - 4
Multiplication
2 * 3.4
Division
9 / 2.0
Remainder
13 % 3
Arithmetic operators.
// gives 16.9
// gives -0.02
// gives 6.8
// gives 4.5
//gives 1
Except for remainder (%) all other arithmetic operators can accept a mix of integer and real
operands. Generally, if both operands are integers then the result will be an integer.
However, if one or both of the operands are reals then the result will be a real (or double to
be exact).
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When both operands of the division operator (/) are integers then the division is performed
as an integer division and not the normal division we are used to. Integer division always
results in an integer outcome (i.e., the result is always rounded down). For example:
9 / 2
-9 / 2
// gives 4, not 4.5!
// gives -5, not -4!
Unintended integer divisions are a common source of programming errors. To obtain a real
division when both operands are integers, you should cast one of the operands to be real:
int
cost = 100;
int
volume = 80;
double unitPrice = cost / (double) volume;
// gives 1.25
The remainder operator (%) expects integers for both of its operands. It returns the
remainder of integer-dividing the operands. For example 13%3 is calculated by integer
dividing 13 by 3 to give an outcome of 4 and a remainder of 1; the result is therefore 1.
It is possible for the outcome of an arithmetic operation to be too large for storing in a
designated variable. This situation is called an overflow. The outcome of an overflow is
machine-dependent and therefore undefined. For example:
unsigned char
k = 10 * 92;
// overflow: 920 > 255
It is illegal to divide a number by zero. This results in a run-time division-by-zero failure,
which typically causes the program to terminate.
There are also a number of predefined library functions, which perform arithmetic
operations. As with input & output statements, if you want to use these you must put a
#include statement at the start of your program. Some of the more common library
functions
are
summarized
as
Parameter
1.6 Result
Type(s)
1.4 Header
File
1.5 Function
<stdlib.h>
abs(i)
int
int
<math.h>
cos(x)
float
float
<math.h>
fabs(x)
float
float
Type
25
follow
1.7 Result
Absolute value of
i
Cosine of x (x is
in radians)
Absolute value of
Department of CS
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<math.h>
pow(x, y)
float
float
<math.h>
sin(x)
float
float
<math.h>
<math.h>
sqrt(x)
tan(x)
float
float
float
float
x
x raised to the
power of y
Sine of x (x is in
radians)
Square root of x
Tangent of x
2.6.3. Relational Operators
C++ provides six relational operators for comparing numeric quantities. These are
summarized in table below. Relational operators evaluate to 1 (representing the true
outcome) or 0 (representing the false outcome).
Operator
==
!=
<
<=
>
>=
Name
Example
Equality
5 == 5
// gives 1
Inequality
5 != 5
// gives 0
Less Than
5 < 5.5 // gives 1
Less Than or Equal
5 <= 5
// gives 1
Greater Than
5 > 5.5 // gives 0
Greater Than or Equal
6.3 >= 5
// gives 1
Relational operators
Note that the <= and >= operators are only supported in the form shown. In particular, =<
and => are both invalid and do not mean anything.
The operands of a relational operator must evaluate to a number. Characters are valid
operands since they are represented by numeric values. For example (assuming ASCII
coding):
'A' < 'F'
// gives 1 (is like 65 < 70)
The relational operators should not be used for comparing strings, because this will result
in the string addresses being compared, not the string contents. For example, the expression
"HELLO" < "BYE" causes the address of "HELLO" to be compared to the address of
"BYE". As these addresses are determined by the compiler (in a machine-dependent
manner), the outcome may be 0 or 1, and is therefore undefined. C++ provides library
functions (e.g., strcmp) for the lexicographic comparison of string.
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2.6.4. Logical Operators
C++ provides three logical operators for combining logical expression. These are
summarized in the table below. Like the relational operators, logical operators evaluate to 1
or 0.
Operator
!
&&
||
Name
Logical Negation
Logical And
Logical Or
Example
!(5 == 5)
// gives 0
5 < 6 && 6 < 6
// gives 1
5 < 6 || 6 < 5 // gives 1
Logical negation is a unary operator, which negates the logical value of its single operand.
If its operand is nonzero it produces 0, and if it is 0 it produces 1.
Logical and produces 0 if one or both of its operands evaluate to 0. Otherwise, it produces
1.
Logical or produces 0 if both of its operands evaluate to 0. Otherwise, it produces 1.
Note that here we talk of zero and nonzero operands (not zero and 1). In general, any
nonzero value can be used to represent the logical true, whereas only zero represents the
logical false. The following are, therefore, all valid logical expressions:
!20
10 && 5
10 || 5.5
10 && 0
// gives 0
// gives 1
// gives 1
// gives 0
2.6.5. Bitwise Operators
C++ provides six bitwise operators for manipulating the individual bits in an integer
quantity. These are summarized in the table below.
Operator
~n
&
|
^
<<
>>
Name
Example
Bitwise Negation
~'\011'
// gives '\366'
Bitwise And
'\011' & '\027' // gives '\001'
Bitwise Or
'\011' | '\027' // gives '\037'
Bitwise Exclusive '\011' ^ '\027' // gives '\036'
Or
Bitwise Left Shift
'\011' << 2
// gives '\044'
Bitwise Right Shift '\011' >> 2
// gives '\002'
Bitwise operators
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Bitwise operators expect their operands to be integer quantities and treat them as bit
sequences. Bitwise negation is a unary operator which reverses the bits in its operands.
Bitwise and compares the corresponding bits of its operands and produces a 1 when both
bits are 1, and 0 otherwise. Bitwise or compares the corresponding bits of its operands and
produces a 0 when both bits are 0, and 1 otherwise. Bitwise exclusive or compares the
corresponding bits of its operands and produces a 0 when both bits are 1 or both bits are 0,
and 1 otherwise.
Bitwise left shift operator and bitwise right shift operator both take a bit sequence as their
left operand and a positive integer quantity n as their right operand. The former produces a
bit sequence equal to the left operand but which has been shifted n bit positions to the left.
The latter produces a bit sequence equal to the left operand but which has been shifted n bit
positions to the right. Vacated bits at either end are set to 0.
Table 2.1 illustrates bit sequences for the sample operands and results in Table 2.Error!
Bookmark not defined.. To avoid worrying about the sign bit (which is machine
dependent), it is common to declare a bit sequence as an unsigned quantity:
unsigned char x = '\011';
unsigned char y = '\027';
Table 2.1
Example
X
Y
~x
x&y
x|y
x^y
x << 2
x >> 2
How the bits are calculated.
Octal Value
011
027
366
001
037
036
044
002
Bit Sequence
0 0 0 0
0 0 0 1
1 1 1 1
0 0 0 0
0 0 0 1
0 0 0 1
0 0 1 0
0 0 0 0
1
0
0
0
1
1
0
0
0
1
1
0
1
1
1
0
0
1
1
0
1
1
0
1
1
1
0
1
1
0
0
0
2.6.6. Increment/decrement Operators
The auto increment (++) and auto decrement (--) operators provide a convenient way of,
respectively, adding and subtracting 1 from a numeric variable. These are summarized in
the following table. The examples assume the following variable definition:
int k = 5;
Operator
Name
Example
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++
++
Auto Increment (prefix)
Auto Increment (postfix)
++k + 10
k++ + 10
---
Auto Decrement (prefix)
--k + 10
Auto Decrement (postfix)
k-- + 10
Increment and decrement operators
// gives 16
// gives 15
// gives 14
// gives 15
Both operators can be used in prefix and postfix form. The difference is significant. When
used in prefix form, the operator is first applied and the outcome is then used in the
expression. When used in the postfix form, the expression is evaluated first and then the
operator applied. Both operators may be applied to integer as well as real variables,
although in practice real variables are rarely useful in this form.
2.7. Precedence of Operators
The order in which operators are evaluated in an expression is significant and is determined
by precedence rules. These rules divide the C++ operators into a number of precedence
levels. Operators in higher levels take precedence over operators in lower levels.
Level
Highest
Operator
::
Kind
Order
Unary
Both
Binary
Left to Right
Unary
Right to Left
Binary
Left to Right
Binary
Left to Right
()
[]
->
.
+
++
!
*
new
-
--
~
&
delete
->*
.*
*
/
+
-
Binary
Left to Right
<<
>>
Binary
Left to Right
<
<=
Binary
Left to Right
==
!=
Binary
Left to Right
&
Binary
Left to Right
^
Binary
Left to Right
|
Binary
Left to Right
&
Binary
Left to Right
Binary
Left to Right
%
>
>=
sizeof()
&
||
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?:
=
Lowest
+=
*=
^=
&=
<<=
-=
/=
%=
=
>>=
,
Ternary
Left to Right
Binary
Right to Left
Binary
Left to Right
For example, in
a == b + c * d
c * d is evaluated first because * has a higher precedence than + and ==. The result is then
added to b because + has a higher precedence than ==, and then == is evaluated.
Precedence rules can be overridden using brackets. For example, rewriting the above
expression as
a == (b + c) * d
causes + to be evaluated before *.
Operators with the same precedence level are evaluated in the order specified by the last
column of Table 2.7. For example, in
a = b += c
the evaluation order is right to left, so first b += c is evaluated, followed by a = b.
2.8. Simple Type Conversion
A value in any of the built-in types we have see so far can be converted (type-cast) to any
of the other types. For example:
(int) 3.14
// converts 3.14 to an int to give 3
(long) 3.14
// converts 3.14 to a long to give 3L
(double) 2
// converts 2 to a double to give 2.0
(char) 122
// converts 122 to a char whose code is 122
(unsigned short) 3.14
// gives 3 as an unsigned short
As shown by these examples, the built-in type identifiers can be used as type operators.
Type operators are unary (i.e., take one operand) and appear inside brackets to the left of
their operand. This is called explicit type conversion. When the type name is just one word,
an alternate notation may be used in which the brackets appear around the operand:
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Fundamental of Programming - I
// same as: (int) 3.14
In some cases, C++ also performs implicit type conversion. This happens when values of
different types are mixed in an expression. For example:
double d = 1;
int
i = 10.5;
i = i + d;
// d receives 1.0
// i receives 10
// means: i = int(double(i) + d)
In the last example, i + d involves mismatching types, so i is first converted to double
(promoted) and then added to d. The result is a double which does not match the type of i
on the left side of the assignment, so it is converted to int (demoted) before being assigned
to i.
The above rules represent some simple but common cases for type conversion.
2.9. Statements
This chapter introduces the various forms of C++ statements for composing programs.
Statements represent the lowest-level building blocks of a program. Roughly speaking,
each statement represents a computational step which has a certain side-effect. (A sideeffect can be thought of as a change in the program state, such as the value of a variable
changing because of an assignment.) Statements are useful because of the side-effects they
cause, the combination of which enables the program to serve a specific purpose (e.g., sort
a list of names).
A running program spends all of its time executing statements. The order in which
statements are executed is called flow control (or control flow). This term reflect the fact
that the currently executing statement has the control of the CPU, which when completed
will be handed over (flow) to another statement. Flow control in a program is typically
sequential, from one statement to the next, but may be diverted to other paths by branch
statements. Flow control is an important consideration because it determines what is
executed during a run and what is not, therefore affecting the overall outcome of the
program.
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Like many other procedural languages, C++ provides different forms of statements for
different purposes. Declaration statements are used for defining variables. Assignment-like
statements are used for simple, algebraic computations. Branching statements are used for
specifying alternate paths of execution, depending on the outcome of a logical condition.
Loop statements are used for specifying computations which need to be repeated until a
certain logical condition is satisfied. Flow control statements are used to divert the
execution path to another part of the program. We will discuss these in turn.
2.9.1. Input/Output Statements
The most common way in which a program communicates with the outside world is
through simple, character-oriented Input/Output (IO) operations. C++ provides two useful
operators for this purpose: >> for input and << for output. We have already seen examples
of output using <<. Example 2.1 also illustrates the use of >> for input.
Example
#include <iostream.h>
int main (void)
{
int
workDays = 5;
float
workHours = 7.5;
float
payRate, weeklyPay;
cout << "What is the hourly pay rate? ";
cin >> payRate;
weeklyPay = workDays * workHours * payRate;
cout << "Weekly Pay = ";
cout << weeklyPay;
cout << '\n';
}
Analysis
This line outputs the prompt ‗What is the hourly pay rate? ‘ to seek user input.
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This line reads the input value typed by the user and copies it to payRate. The input
operator >> takes an input stream as its left operand (cin is the standard C++ input stream
which corresponds to data entered via the keyboard) and a variable (to which the input data
is copied) as its right operand.
When run, the program will produce the following output (user input appears in bold):
What is the hourly pay rate? 33.55
Weekly Pay = 1258.125
Both << and >> return their left operand as their result, enabling multiple input or multiple
output operations to be combined into one statement. This is illustrated by example below
which now allows the input of both the daily work hours and the hourly pay rate.
Example
#include <iostream.h>
int main (void)
{
int
float
workDays = 5;
workHours, payRate, weeklyPay;
cout << "What are the work hours and the hourly pay rate? ";
cin >> workHours >> payRate;
weeklyPay = workDays * workHours * payRate;
cout << "Weekly Pay = " << weeklyPay << '\n';
}
Analysis
This line reads two input values typed by the user and copies them to workHours and
payRate, respectively. The two values should be separated by white space (i.e., one or more
space or tab characters). This statement is equivalent to:
(cin >> workHours) >> payRate;
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Because the result of >> is its left operand, (cin >> workHours) evaluates to cin which is
then used as the left operand of the next >> operator.
This line is the result of combining lines 10-12 from example 2.1. It outputs "Weekly Pay =
", followed by the value of weeklyPay, followed by a newline character. This statement is
equivalent to:
((cout << "Weekly Pay = ") << weeklyPay) << '\n';
Because the result of << is its left operand, (cout << "Weekly Pay = ") evaluates to cout
which is then used as the left operand of the next << operator, etc.
When run, the program will produce the following output:
What are the work hours and the hourly pay rate? 7.5 33.55
Weekly Pay = 1258.125
2.9.2. Null statement
Syntax:
;
Description:
Do nothing
2.9.3. The block statement
Syntax:
{
[<Declarations>].
<List of statements/statement block>.
}
Any place you can put a single statement, you can put a compound statement, also called a
block. A block begins with an opening brace ({) and ends with a closing brace (}).
Although every statement in the block must end with a semicolon, the block itself does not
end with a semicolon. For example
{
temp = a;
a = b;
b = temp;
}
This block of code acts as one statement and swaps the values in the variables a and b.
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2.9.4. The Assignment statement.
Syntax:
<Variable Identifier> = < expression>;
Description:
The <expression> is evaluated and the resulting value is stored in the memory space
reserved for <variable identifier>.
Eg: - int x,y ;
x=5;
y=x+3;
x=y*y;
3. Control Statements
3.1. Introduction
A running program spends all of its time executing statements. The order in which
statements are executed is called flow control (or control flow). This term reflect the fact
that the currently executing statement has the control of the CPU, which when completed
will be handed over (flow) to another statement. Flow control in a program is typically
sequential, from one statement to the next, but may be diverted to other paths by branch
statements. Flow control is an important consideration because it determines what is
executed during a run and what is not, therefore affecting the overall outcome of the
program.
Like many other procedural languages, C++ provides different forms of statements for
different purposes. Declaration statements are used for defining variables. Assignmentlike statements are used for simple, algebraic computations. Branching statements are
used for specifying alternate paths of execution, depending on the outcome of a logical
condition. Loop statements are used for specifying computations, which need to be
repeated until a certain logical condition is satisfied. Flow control statements are used to
divert the execution path to another part of the program. We will discuss these in turn.
3.2. Conditional Statements
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3.2.1. The if Statement
It is sometimes desirable to make the execution of a statement dependent upon a
condition being satisfied. The if statement provides a way of expressing this, the general
form of which is:
if (expression)
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statement;
First expression is evaluated. If the outcome is nonzero (true) then statement is executed.
Otherwise, nothing happens.
For example, when dividing two values, we may want to check that the denominator is
nonzero:
if (count != 0)
average = sum / count;
To make multiple statements dependent on the same condition, we can use a compound
statement:
if (balance > 0) {
interest = balance * creditRate;
balance += interest;
}
A variant form of the if statement allows us to specify two alternative statements: one
which is executed if a condition is satisfied and one which is executed if the condition is
not satisfied. This is called the if-else statement and has the general form:
if (expression)
statement1;
else
statement2;
First expression is evaluated. If the outcome is nonzero (true) then statement1 is
executed. Otherwise, statement2 is executed.
For example:
if (balance > 0) {
interest = balance * creditRate;
balance += interest;
} else {
interest = balance * debitRate;
balance += interest;
}
Given the similarity between the two alternative parts, the whole statement can be
simplified to:
if (balance > 0)
interest = balance * creditRate;
else
interest = balance * debitRate;
balance += interest;
Or simplified even further using a conditional expression:
interest = balance * (balance > 0 ? creditRate : debitRate);
balance += interest;
Or just:
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balance += balance * (balance > 0 ? creditRate : debitRate);
If statements may be nested by having an if statement appear inside another if statement.
For example:
if (callHour > 6) {
if (callDuration <= 5)
charge = callDuration * tarrif1;
else
charge = 5 * tarrif1 + (callDuration - 5) * tarrif2;
} else
charge = flatFee;
A frequently-used form of nested if statements involves the else part consisting of
another if-else statement. For example:
if (ch >= '0' && ch <= '9')
kind = digit;
else {
if (ch >= 'A' && ch <= 'Z')
kind = upperLetter;
else {
if (ch >= 'a' && ch <= 'z')
kind = lowerLetter;
else
kind = special;
}
}
For improved readability, it is conventional to format such cases as follows:
if (ch >= '0' && ch <= '9')
kind = digit;
else if (cha >= 'A' && ch <= 'Z')
kind = capitalLetter;
else if (ch >= 'a' && ch <= 'z')
kind = smallLetter;
else
kind = special;
3.2.2. The switch Statement
The switch statement provides a way of choosing between a set of alternatives, based on
the value of an expression. The general form of the switch statement is:
switch (expression) {
case constant1:
statements;
...
case constantn:
statements;
default:
statements;
}
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First expression (called the switch tag) is evaluated, and the outcome is compared to each
of the numeric constants (called case labels), in the order they appear, until a match is
found. The statements following the matching case are then executed. Note the plural:
each case may be followed by zero or more statements (not just one statement).
Execution continues until either a break statement is encountered or all intervening
statements until the end of the switch statement are executed. The final default case is
optional and is exercised if none of the earlier cases provide a match.
For example, suppose we have parsed a binary arithmetic operation into its three
components and stored these in variables operator, operand1, and operand2. The following
switch statement performs the operation and stores the result in result.
switch (operator) {
case '+':
result = operand1 + operand2;
break;
case '-':
result = operand1 - operand2;
break;
case '*':
result = operand1 * operand2;
break;
case '/':
result = operand1 / operand2;
break;
default:cout << "unknown operator: " << ch << '\n';
break;
}
As illustrated by this example, it is usually necessary to include a break statement at the
end of each case. The break terminates the switch statement by jumping to the very end
of it. There are, however, situations in which it makes sense to have a case without a
break. For example, if we extend the above statement to also allow x to be used as a
multiplication operator, we will have:
switch (operator) {
case '+':
result = operand1 + operand2;
break;
case '-':
result = operand1 - operand2;
break;
case 'x':
case '*':
result = operand1 * operand2;
break;
case '/':
result = operand1 / operand2;
break;
default:cout << "unknown operator: " << ch << '\n';
break;
}
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Because case 'x' has no break statement (in fact no statement at all!), when this case is
satisfied, execution proceeds to the statements of the next case and the multiplication is
performed.
It should be obvious that any switch statement can also be written as multiple if-else
statements. The above statement, for example, may be written as:
if (operator == '+')
result = operand1 + operand2;
else if (operator == '-')
result = operand1 - operand2;
else if (operator == 'x' || operator == '*')
result = operand1 * operand2;
else if (operator == '/')
result = operand1 / operand2;
else
cout << "unknown operator: " << ch << '\n';
However, the switch version is arguably neater in this case. In general, preference should
be given to the switch version when possible. The if-else approach should be reserved for
situation where a switch cannot do the job (e.g., when the conditions involved are not
simple equality expressions, or when the case labels are not numeric constants).
3.3. Looping Statements
3.3.1. The ‘while’ Statement
The while statement (also called while loop) provides a way of repeating a statement
while a condition holds. It is one of the three flavours of iteration in C++. The general
form of the while statement is:
while (expression)
{
statement;
}
First expression (called the loop condition) is evaluated. If the outcome is nonzero then
statement (called the loop body) is executed and the whole process is repeated.
Otherwise, the loop is terminated.
For example, suppose we wish to calculate the sum of all numbers from 1 to some integer
denoted by n. This can be expressed as:
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i = 1;
sum = 0;
while (i <= n)
{
sum += i;
}
For n set to 5, Table 2.9 provides a trace of the loop by listing the values of the variables
involved and the loop condition.
Iteration
First
Second
Third
Fourth
Fifth
Sixth
Table 5.1
i
1
2
3
4
5
6
While loop trace
n
i <= n
sum += i++
5
1
1
5
1
3
5
1
6
5
1
10
5
1
15
5
0
It is not unusual for a while loop to have an empty body (i.e., a null statement).
3.3.2. The ‘for’ Statement
The for statement (also called for loop) is similar to the while statement, but has two
additional components: an expression which is evaluated only once before everything
else, and an expression which is evaluated once at the end of each iteration. The general
form of the for statement is:
for (expression1; expression2; expression3)
{
statement;
}
First expression1 is evaluated. Each time round the loop, expression2 is evaluated. If the
outcome is nonzero then statement is executed and expression3 is evaluated. Otherwise, the
loop is terminated. The general for loop is equivalent to the following while loop:
expression1;
while (expression2) {
statement;
expression3;
}
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The most common use of for loops is for situations where a variable is incremented or
decremented with every iteration of the loop. The following for loop, for example,
calculates the sum of all integers from 1 to n.
sum = 0;
for (i = 1; i <= n; ++i)
{
sum += i;
}
This is preferred to the while-loop version we saw earlier. In this example, i is usually
called the loop variable.
C++ allows the first expression in a for loop to be a variable definition. In the above loop,
for example, i can be defined inside the loop itself:
for (int i = 1; i <= n; ++i)
{
sum += i;
}
Contrary to what may appear, the scope for i is not the body of the loop, but the loop
itself. Scope-wise, the above is equivalent to:
int i;
for (i = 1; i <= n; ++i)
sum += i;
Any of the three expressions in a for loop may be empty. For example, removing the first
and the third expression gives us something identical to a while loop:
for (; i != 0;)
something;
// is equivalent to: while (i != 0)
//
something;
Removing all the expressions gives us an infinite loop. This loop's condition is assumed
to be always true:
for (;;)
something;
// infinite loop
For loops with multiple loop variables are not unusual. In such cases, the comma operator
is used to separate their expressions:
for (i = 0, j = 0; i + j < n; ++i, ++j)
something;
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Because loops are statements, they can appear inside other loops. In other words, loops
can be nested. For example,
for (int i = 1; i <= 3; ++i)
for (int j = 1; j <= 3; ++j)
cout << '(' << i << ',' << j << ")\n";
produces the product of the set {1,2,3} with itself, giving the output:
(1,1)
(1,2)
(1,3)
(2,1)
(2,2)
(2,3)
(3,1)
(3,2)
(3,3)
3.3.3. The ‘do…while’ Statement
The do statement (also called do loop) is similar to the while statement, except that its
body is executed first and then the loop condition is examined. The general form of the
do statement is:
do
statement;
while (expression);
First statement is executed and then expression is evaluated. If the outcome of the latter is
nonzero then the whole process is repeated. Otherwise, the loop is terminated.
The do loop is less frequently used than the while loop. It is useful for situations where
we need the loop body to be executed at least once, regardless of the loop condition. For
example, suppose we wish to repeatedly read a value and print its square, and stop when
the value is zero. This can be expressed as the following loop:
do {
cin >> n;
cout << n * n << '\n';
} while (n != 0);
Unlike the while loop, the do loop is never used in situations where it would have a null
body. Although a do loop with a null body would be equivalent to a similar while loop,
the latter is always preferred for its superior readability.
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3.4. Other Statements
3.4.1. The ‘continue’ Statement
The continue statement terminates the current iteration of a loop and instead jumps to
the next iteration. It applies to the loop immediately enclosing the continue statement. It
is an error to use the continue statement outside a loop.
In while and do loops, the next iteration commences from the loop condition. In a for
loop, the next iteration commences from the loop‘s third expression. For example, a loop
which repeatedly reads in a number, processes it but ignores negative numbers, and
terminates when the number is zero, may be expressed as:
do {
cin >> num;
if (num < 0) continue;
// process num here...
} while (num != 0);
This is equivalent to:
do {
cin >> num;
if (num >= 0) {
// process num here...
}
} while (num != 0);
A variant of this loop which reads in a number exactly n times (rather than until the
number is zero) may be expressed as:
for (i = 0; i < n; ++i) {
cin >> num;
if (num < 0) continue;
// process num here...
}
// causes a jump to: ++i
When the continue statement appears inside nested loops, it applies to the loop
immediately enclosing it, and not to the outer loops. For example, in the following set of
nested loops, the continue applies to the for loop, and not the while loop:
while (more) {
for (i = 0; i < n; ++i) {
cin >> num;
if (num < 0) continue;
// process num here...
}
//etc...
}
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3.4.2. The ‘break’ Statement
A break statement may appear inside a loop (while, do, or for) or a switch statement. It
causes a jump out of these constructs, and hence terminates them. Like the continue
statement, a break statement only applies to the loop or switch immediately enclosing it.
It is an error to use the break statement outside a loop or a switch.
For example, suppose we wish to read in a user password, but would like to allow the
user a limited number of attempts:
for (i = 0; i < attempts; ++i) {
cout << "Please enter your password: ";
cin >> password;
if (Verify(password))
// check password for correctness
break;
// drop out of the loop
cout << "Incorrect!\n";
}
Here we have assumed that there is a function called Verify which checks a password
and returns true if it is correct, and false otherwise.
Rewriting the loop without a break statement is always possible by using an additional
logical variable (verified) and adding it to the loop condition:
verified = 0;
for (i = 0; i < attempts && !verified; ++i) {
cout << "Please enter your password: ";
cin >> password;
verified = Verify(password));
if (!verified)
cout << "Incorrect!\n";
}
The break version is arguably simpler and therefore preferred.
3.4.3. The ‘goto’ Statement
The goto statement provides the lowest-level of jumping. It has the general form:
goto label;
where label is an identifier which marks the jump destination of goto. The label should be
followed by a colon and appear before a statement within the same function as the goto
statement itself. For example, the role of the break statement in the for loop in the
previous section can be emulated by a goto:
for (i = 0; i < attempts; ++i) {
cout << "Please enter your password: ";
cin >> password;
if (Verify(password))
// check password for correctness
goto out;
// drop out of the loop
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cout << "Incorrect!\n";
}
out:
//etc...
Because goto provides a free and unstructured form of jumping (unlike break and
continue), it can be easily misused. Most programmers these days avoid using it
altogether in favor of clear programming. Nevertheless, goto does have some legitimate
(though rare) uses.
3.4.4. The ‘return’ Statement
The return statement enables a function to return a value to its caller. It has the general
form:
return expression;
where expression denotes the value returned by the function. The type of this value
should match the return type of the function. For a function whose return type is void,
expression should be empty:
return;
The only function we have discussed so far is main, whose return type is always int. The
return value of main is what the program returns to the operating system when it
completes its execution. Under UNIX, for example, it its conventional to return 0 from
main when the program executes without errors. Otherwise, a non-zero error code is
returned. For example:
int main (void)
{
cout << "Hello World\n";
return 0;
}
When a function has a non-void return value (as in the above example), failing to return a
value will result in a compiler warning. The actual return value will be undefined in this
case (i.e., it will be whatever value which happens to be in its corresponding memory
location at the time).
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