Overview of C++
Chapter 2
2.1 C++ Language Elements




Comments make a program easier to
understand
// Used to signify a comment on a single
line
/* Text text */ use if comments on multi
lines
Don’t embed comments within /* */
comments
2
Compiler Directives

#include
– Compiler directive
– (Pre-)Processed at compilation time
– Instructs compiler on what you want to include in the
program

#include <iostream>
– Adds library files to program
– Used with < >
– Also “ “ user defined
3
Compiler Directives

Stream data type
– Delivers objects that are streams of characters
– Defined in iostream
– Entered on the keyboard (cin)
– Displayed on monitor
(cout)
4
Namespace std






Name region
Standard library is defined in std
Always: using namespace std;
Attention for the “;” after the declaration
Compare: No “;” for include directives
Should follow include-lines
5
The Function “main”

Form:
– int main()




Indicates where the program starts
Must be included in EVERY C++ program
Function: A named sequence of statements
which can be called and parameterized.
int: Return type of the program (for the
operating system)
6
Declarations

Function body:
– Declaration statements
– Executable statements


Declarations specify data needs (data identifiers)
Each identifier needed must be declared
– const float Km_Per_Mile = 1.609;

Comma used to separate identifiers
– float miles, km;

cin and cout are undeclared identifiers
– Special elements called streams (included with the
iostream)
– cin - input stream , cout - output stream
7
Executable Statements

cout diplays output
– cout << “Enter the fabric size in square
meters: ”;

cin gets input
– cin >> sizeInSqmeters;

Assignment
– sizeInSqyards = metersToYards * sizeInSqmeters;
8
2.2 Reserved Words and
Identifiers

Reserved words have special meanings
– Can NOT be used for other purposes (const, float
and void are some examples)

Identifiers (variables)
– Used to store data by the program (user-defined)
– Valid identifiers - letter, letter1, _letter
– Invalid identifiers - 1letter, const, hell o
9
Reserved Words and
Identifiers

Special symbols
– C++ has rules for special symbols
– = * ; { } ( ) // << >>

Appendix B
– Examples of reserved words
– Special characters
10
Upper and Lower Case

C++ case sensitive
– Compiler differentiates upper & lower case
– Identifiers can be either
– Be careful though (cost != Cost)

Blank spaces and tabs
– Use space to make program readable
– Use care in placing spaces

Usually (C-style):
– Constants: Upper Case (e.g. TIME_TO_TRAVEL)
– Identifier: Lower Case (e.g. time_to_travel or better
timeToTravel)
11
2.3 Data Types and
Declarations

Data type:
– Set of values an operations that can be performed on
these values

Predefined data types
– int
(integers)
• Positive or negative whole numbers
• -1000 12
199
100000
• INT_MAX
- largest int allowed by compiler
– float
(real numbers)
• Positive or negative decimal numbers
• -10.5
1.2
100.02
99.88
12
Data Types and Declarations

Predefined data types
– bool
(boolean)
• true
• false
– char
(Characters)
• Represent characters (keyboard symbols)
13
Data Types and Declarations

The basic integer type is int
– The size of an int depends on the machine and
the compiler
• On pc’s it is normally 16 or 32 bits

Other integers types
– short: typically uses less bits
– long: typically uses more bits

INT_MIN and INT_MAX
14
Data Types and Declarations



Different types allow programmers to use
resources more efficiently
Standard arithmetic and relational operations are
available for these types
Operations:
–
–
–
–
Addition
Subtraction
Multiplication
…
15
Data Types and Declarations

Floating-point types represent real numbers
– Integer part
– Fractional part

The number 108.1517 breaks down into the
following parts
– 108 - integral part
– 1517 - fractional part

Examples
-10.67
.6789
75.
3.366
16
Data Types and Declarations

C++ provides three floating-point types
– float
– double
– long double

Scientific notation possible:
1.56*106 in C++: 1.56e6 or 1.56e+6




e: lower case exponent
Exponent whole number (int)
Fixed point format for integers  binary number
Floating point format for real number 
0.5 <= mantissa <= 1.0 and an integer exponent (basis 2)
17
Data Types and Declarations

Predefined data types
– char
(characters)
• Individual character value (letter or number)
• Character literal enclosed in single quotes ‘A’
• Escape sequences: ‘\n’ ‘\b’ ‘\r’ ‘\t’ ‘\\’
– bool
(true / false)
18
Data Types and Declarations


ASCII is the dominant encoding scheme
One byte a character (Unicode more bytes)
– Examples
•
•
•
•
•
•
' ' encoded as 32
'+' encoded as 43
'A' encoded as 65
'Z' encoded as 90
’a' encoded as 97
’z' encoded as 122
19
Why Data Types




Compiler knows about correct values and
operations
Minimize resources
Early failure detection
Examples of failures:
– n = true+false;
– If(2 == ‘2’)
20
string Class

String object data type
– A literal string constant is a sequence of zero or
more characters enclosed in double quotes
– “I am a string\n"
– Individual characters of string are stored in
consecutive memory locations
– The null character ('\0') is appended to strings
so that the compiler knows where in memory
strings ends
21
string Class

String literal
– “A”
– “1234”
– “Enter the distance”

Additional data types included in library
#include <string>
– Various operations on strings
– Compare, Join, Length, etc.
22
Declarations

Identifiers should be
– Short enough to be reasonable to type (single
word is norm)
• Standard abbreviations are fine (but only standard
abbreviations)
– Long enough to be understandable
• When using multiple word identifiers capitalize the
first letter of each word
23
Variable Declarations



Variable: Name associated with a location
in memory
Variable declaration: Tells compiler the
name and the type of the variable
Examples
–
–
–
–
–
char response;
float temperature;
int i;
string firstName;
bool isAvailable;
24
Variable Declarations

Form:
Type identifier_list;

Examples
int index, value;
string gender = “male”;

Compiler allocates storage for each variable
in the list using the specified data type
information.
25
Constant Declarations

Types of constants
–
–
–
–
–

integer
float
char
bool
string objects
Associate meaningful terms
– const

float
PAYRATE = 10.25;
Interpretation similar to variables with the constraint
that constants can not be changed (read-only!).
26
Hello.cpp
// FILE: Hello.cpp
// DISPLAYS A USER'S NAME
#include <iostream>
#include <string>
using namespace std;
int main ()
{
27
Hello.cpp
char letter1, letter2;
string lastName;
// Enter letters and print message.
cout << "Enter 2 initials and last name: ";
cin >> letter1 >> letter2 >> lastName;
cout << "Hello " << letter1 << ". " <<
letter2 << ". " << lastName << "! ";
cout << "We hope you enjoy studying C++." <<
endl;
return 0;
}
28
Hello.cpp
Program output
Enter first two initials and last name and press
return: EBKoffman
Hello E. B. Koffman! We hope you enjoy
studying C++.
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2.4 Executable Statements

Executable Statement:
C++ statement that is translated into a sequence of machine
language instructions.

Memory status: e.g. miles-to-km conversion program
– Before execution:
– After execution:

miles = ?
kms = ?
miles = 10.00 kms = 16.09
Assignments
– Form: result = expression;
– kms = KM_PER_METER * miles;
– sum = sum + item;
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2.4 Executable Statements

Example 1:
kms = KM_PER_METER * miles;
Before assignment
After assignment
KMS_PER_
MILE
1.609
1.609
*
miles
10.00
10.00
kms
?
16.09
31
2.4 Executable Statements

Example 2:
x = x + n;
Not an algebraic equation!!
Before assignment
After assignment
x
20
25
+
n
5
5
32
Arithmetic Operators
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



+
*
/
%
Addition
Subtraction
Multiplication
Division
Modulus
33
Input / Output Operations

Input
– #include <iostream> library
– cin >> sizeInSqmeters;




Extracted from cin (input stream)
>> Directs input to variable
cin associated with keyboard input (stdin)
Used with int, float, char, bool and strings
34
Data Types and cin

Don’t mix types with cin
int x;
cin >> x;
Keyboard input
16.6
Value placed in x would be 16
35
Other Characteristics of cin




Leading blanks ignored (floats, int, char,
bool and strings)
Char read 1 at a time (1 non blank)
int or float will read until space or carriage
return
Stings same as int and float
36
General Form for cin

Form: cin >> dataVariable;
cin >> age >> firstInitial;

How does the user know when to type in some
data?
 Your program must prompt for that (output)
37
Program Output


Output stream cout
<< Output operator (insertion operator)
– cout << “my height in inches is: “ << height;

Blank lines
– endl; or “\n”;


Form: cout << dataVariable;
Example:
cout << “Hello Mr. “ << name << “ !!\n”
38
Return Statement

Form:
return expression;

Expression:
–
–
–
–
Literal
Variable
Arithmetic
Logic
 Examples: return 0;
return x + z;

Return: Transfers control to the caller of the
function (in case of the function main the caller is
the operating system)
39
2.5 General Form of a C++
Program

General program form
– Function: basic unit (collection of related
statements)
– A C++ program must contain a main function
void main ()
– int - function returns integer value
– main - lower case with ()
– { } - Braces define the function body
40
General Form of a C++
Program

General form of function body parts
– Declaration statements
• Variables and constants
– Executable statements
• C++ statements
41
General Form of a C++
Program

General form
// File: filename
// Program description:
#include directives
int main()
{
Declarations section
Executable statements section
}
42
General Form
// Name: Mike Hudock
// Date: March 10, 2000
// Files: file1.cpp
file2.cpp
// Changes :
// Program description:
43
General Form




Use comments throughout code to highlight
points of interest
Avoid strange identifiers
Function explanations
Algorithm definitions
44
2.6 Arithmetic Expressions

int data type
– + - * /, Assignment, input and output on int
– %
Only used with int

Examples of integer division (only integral part is
considered)
15 / 3 = 5
15 / 2 = 7
17/-2 system dependent (avoid it!)
0 / 15 = 0
15 / 0 undefined
45
Modulus and Integer




Used only with integer and yields remainder
Examples of integer modulus
7%2=1
299 % 100 = 99
49 % 5 = 4
33%-2 varies among implementations (avoid negative
numbers!)
15 % 0 undefined
0<= m%n < n
Relationship:
m == (m/n)*n + m%n
46
Mixed-type Assignments


Mixed-type expression: An expression including
operands of type int and float.
What is the type of an expression?
– Variable type are specified in their declarations.
– An expression is of type int iff all operands are of type
int.
– If at least one operand is float the expression becomes
type float.

Examples: 5/2 is int, 5/2.0 is float
47
Mixed-type Assignments




Conversion from int to float is needed in
evaluating mixed-type expressions.
Eg. 5/2.0 becomes 5.0/2.0
Assignment: First right side is evaluated, then the
result is assigned to the left side.
Examples for mixed-type assignments:
float rate = 100;
rate = 100/3;
// Value of rate: 100.0
// Value of rate: 33.0
// (common error: rate = 33.33..)
48
Mixed-type Assignments

Another example:
int n;
n = 15.7 + 3.5;
// Value of n is integral part of the
// sum 19.2 which is 19  n = 19
// Be careful: n != 15 + 3 = 18
49
Expressions With Multiple
Operators


Operator precedence tells how to evaluate
expressions
Standard precedence order:
–
–
–
–
1. ( ): if nested then innermost first
2. Unary + - : if multiple then from right to left
3. * / %: If several then from left to right
4. Binary + -: If several then from left-to-right
50
Evaluation of Expressions

z - (a + b ) + w * -y (all variables are int)
2


C++ notation: z – (a+b/2)+w*-y
1. Rule 1  term a+b/2 first
2. Rule 3  / before +  evaluate b/2
3. Rule 4  evaluate a + b/2
4. Rule 2  evaluate –y
5. Rule 3  evaluate w*-y
6. Rule 4  evaluate z – (a+b/2) [left first!]
7. Rule 4  evaluate whole expression
51
Evaluation of Expressions


Mixed-type evaluation
is more tricky!
Example:
int m, k;
float x;
k = 5;
x = 5.5;
m = x + k/2

Evaluation:
1. Rule 3  / before + 
evaluate k/2 and get 2
(since k is int!)
2. Rule 4  evaluate the
whole expression:
2.1 convert 2 to 2.0
2.2 get the sum 7.5
2.3 convert back to int
2.4 store integral part
7 in m
52
Coin Collection Case Study

Problem statement
– Saving nickels and pennies and want to exchange these
coins at the bank so need to know the value of coins in
dollars and cents.

Analysis
– Count of nickels and pennies in total
– Determine total value
• 1 penny = 1 cent
• 1 nickel = 5 pennies
– Use integer division to get dollar value
• / 100
53
Coin Collection Case Study

Analysis (cont)
– Use modulus % to get cents value
– % 100

Design
–
–
–
–
–
Prompt for name
Get count of nickels and pennies
Compute total value
Calculate dollars and cents
Display results
54
Coin Collection Case Study

Implementation
– Write C++ code of design
– Verify correct data types needed
– Mixed mode types and promotion

Testing
– Test results using various input combinations
55
Coins.cpp
// File: coins.cpp
// Determines the value of a coin collection
#include <iostream>
#include <string>
using namespace std;
int main()
{
56
Coins.cpp
// Local data ...
string name;
int pennies;
int nickels;
int dollars;
int change;
int totalCents;
// Prompt sister for name.
cout << "Enter your first name: ";
cin >> name;
57
Coins.cpp
// Read in the count of nickels and pennies.
cout << "Enter the number of nickels: ";
cin >> nickels;
cout << "Enter the number of pennies: ";
cin >> pennies;
// Compute the total value in cents.
totalCents = 5 * nickels + pennies;
// Find the value in dollars and change.
dollars = totalCents / 100;
change = totalCents % 100;
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Coins.cpp
// Display the value in dollars and change.
cout << "Good work " << name << '!' << endl;
cout << "Your collection is worth " <<
dollars << " dollars and " <<
change << " cents." << endl;
return 0;
}
59
Coins.cpp
Program output
Enter your first name and press return: Sally
Enter number of nickels and press return: 30
Enter number of pennies and press return: 77
Good work sally!
Your collection is worth 2 dollars and 27
cents.
60
2.7 Interactive Mode, Batch
and Data Files

Two modes interactive or batch
– Keyboard input interactive

Batch mode data provided prior to start
– File as input

Input / output redirection
– Direct input to program use ‘<‘ symbol
– Direct output to a file use ‘>‘ symbol
– Operating system dependent
61
Input / Output Redirection

Input:
– Program name < datafile
– Unix:
metric  awaits data from keyboard
metric < mydata  now from a file named
mydata
62
Input / Output Redirection

Output:
– Program name > outFile
– metric > outFile

Input and output redirection
– metric < inFile > outFile
63
Milesbatch.cpp
// File: milesBatch.cpp
// Converts distance in miles to kilometers.
#include <iostream>
using namespace std;
int main()
// start of main function
{
const float KM_PER_MILE = 1.609;
float miles,
kms;
64
Milesbatch.cpp
// Need not prompt user since input from a file
// Get the distance in miles.
cin >> miles;
cout << "The distance in miles is " <<
miles << endl;
// Convert the distance to kilometers.
kms = KM_PER_MILE * miles;
// Display the distance in kilometers.
cout << "The distance in kilometers is " <<
kms << endl;
return 0;
}
65
Milesbatch.cpp
Program output
The distance in miles is 10
The distance in kilometers is 16.09
66
2.8 Common Programming
Errors

Programming Errors
– Very common
– “Bugs” term for software errors
– Debugging: process of detecting and removing bugs.

Syntax Errors
– Violation of grammatical rules e.g. use of variable
without declaring it first.
– Systematic solutions
– Errors vs. Warnings

Compiler not descriptive
– Look at line number before and after error
– Watch missing ; and }
67
Common Programming Errors

Run-time errors
– Illegal operation (divide by 0)
– Even when a program is syntactically correct, run-time
errors may occur.
– Debugging can help

Logic errors
– Program functions differently than you expect
• Wrong solution for a given (sub)problem !!!
– Thorough testing and desk checking or step-by-step
debugging can help.
68