LECTEURE # 5 :
STRUCTURED PROGRAMMING
Variables , input , memory
Tr.Hadeel
Content
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Variables
C++ Built in data types
C++ variable declaration syntax
cin statement
Local and global variables
Scope resolution operator (::)
Variables and RAM
Defining constants
Typecasting
Enumerated data types
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Variable
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
Location on computer’s memory to store data then use and change
its value in a program
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Each variable has
1.
2.
Name (identifier)
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Series of letters, digits, underscores

Not a keyword
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Start with a letter
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Case sensitive

Meaningful
Type
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Programmer-defined
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Determine which of the following variables name is valid or
invalid :
4
_under_bar_
z2
h22
2h
67h2
his_account_total
t5
87
m928134
her_sales
3g
j7
a
b
c
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C++ Built-in Data Types
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
Called fundamental types or primitives types: numeric, character,
logical
bool Data Type
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Has two values, true and false
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Manipulate logical (Boolean) expressions
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true and false are called logical values
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bool, true, and false are reserved words
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char Data Type
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Used for characters
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Each character is enclosed in single quotes
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letters, digits, and special symbols
Examples: 'A', 'a', '0', '*', '+', '$', '&'
A blank space is a character and is written ' ' with a space left
between the single quotes
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Declaring Variables
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All variables must be declared anywhere in program with a name
and data type before they used
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Syntax rule: begin with a data type then variable name
dataType varName;
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Variables of the same type can be declared in
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Multiple lines
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One line separated by commas
int num1;
int num2;
int num3;
int num1, num2, num3;
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Initializing Variable
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
Variables can be initialized once declared
int first=13, second=10;
char ch=' ';
double x=12.6, y=123.456;

first and second are int variables with the values 13 and 10,
respectively
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ch is a char variable whose value is empty
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x and y are double variables with 12.6 and 123.456, respectively
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Using cin
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Namespace

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std::
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Specifies using a name that belongs to “namespace” std

Can be removed through use of using statements
Standard output stream object
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std::cin
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“Connected” to keyboard
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Defined in input/output stream header file <iostream>
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Using cin (cont.)
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
Stream extraction operator >>
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Value to left (left operand) inserted into right operand
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Waits for user to input value then press Enter key
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Example
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std::cin >> num1;
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Inserts the standard input from keyboard into variable num1

Prints message before cin statement to direct the user to take a
specification called prompt

cin and cout facilitate interaction between user and program
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// Fig. 2.5: fig02_05.cpp
// Addition program that display the sum of two numbers.
#include <iostream> // allow program to perform input and output
// function main begins program execution
int main()
{
Declare integer variables.
// variable declaration
int number1; // first integer to add
int number2; // second integer to add
Use and
stream
extraction
int sum; // sum of number1
number2
std::cout << "Enter
std::cin >> number1;
operator with standard input
to obtain
input. user
first stream
integer:
\n"; user
// prompt
for data
// read first integer from user to number1
Calculations can be performed in output statements: alternative for
std::cout << "Enter second integer: \n"; // prompt user for data
lines 19 and 21:
std::cin >> number2; // read second integer from user to number2
Stream manipulator
std::cout << "Sum is " << number1
+ number2outputs
<< std::endl;
std::endl
a
sum = number1 + number2; // add the numbers; stor result
in sum
newline, then “flushes output
std::cout << "Sum is " << sum << std::endl; // display buffer.”
sum; end line
return 0;
// indicate that program ended successfully
} // end function main
Enter first integer
45
Enter second integer
72
Concatenating, chaining or
cascading stream insertion
operations.
Sum is 117
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Variable Scope
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
Portion of the program where the variable can be used
Scope can be

Local

Global
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Local Variables
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Defined within a module
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Can be seen and used only by module itself
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Store temporally in memory
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Erased when the module terminates
int main()
{
int i;
char a;
return 0;
}
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Global Variables
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Defined outside any module
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Used and seen by all modules
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Variable name can be duplicated within and outside a modules

Differentiate between them by using unary scope resolution operator (::)
int i;
int main()
{
char a;
return 0;
}
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Unary Scope Resolution Operator
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
Denoted as ( :: )

Used to declare local and global variables have a same name


To avoid conflicts
Syntax rule
::variable
y = ::x + 3

Not needed if names are different
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// Fig. 6.23: fig06_23.cpp
// using the unary scope resolution operator.
#include <iostream>
using std::cout;
using std::endl;
int number = 7;
// global variable named number
int main()
{
double number = 10.5;
// local variable named number
// display values of local and global variables
cout <<“local double value of number = “ << number
<< “\nGlobal int value of number = “ << ::number << endl;
return 0;
// indicate successful termination
} // end main
Local double value of number = 10.5
Global int value of number = 7
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Variables and Memory
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
Variables names correspond to location in the computer’s memory
(RAM)

Every variable has name, type, size and value
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Placing new value into variable (memory location), overwrites old
value – called destructive

Reading value of variable in memory – called nondestructive
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Variables and Memory (cont.)
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std::cin >> number1;
Assume user entered 45
std::cin >> number2;
Assume user entered 72
sum = number1 + number2;
number1
45
number1
45
number2
72
number1
45
number2
72
sum
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117
Constants
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
Like variables
 data storage locations

Unlike variables
 Values never changed during program execution
 Any attempt to change a const creates a compilation error
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Declared in two ways and follow identifier naming rules
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With const keyword
const char Gender = ‘F’;
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With #define keyword
#define studentsPerClass 15
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Compatible C++ Data Types
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Data types
Highest
long double
double
float
unsigned long int
(synonymous with unsigned long)
long int
(synonymous with long)
unsigned int
int
(synonymous with unsigned)
unsigned short int
(synonymous with unsigned short)
short int
unsigned char
char
bool
(synonymous with short)
Lowest
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Converting Data Types
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
Convert variables or expression of a given type into another type

Two kinds of conversion
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Implicit conversion
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Explicit conversion
May include
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Promotion: converting from low to high data type
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Demotion: converting from high to low data type
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Implicit Conversion
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Promote to double
Mixed Type Expressions
double
double

avg
=
total
int
/
cnt
;
Assignment statement
int
x
int
=
7.5
;
double
Demote to int  fraction part is truncated
warning : conversion from 'double' to 'int',
possible loss of data
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Explicit Conversion - Typecasting
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
C-like notation
int
a
double
b

=
=
2000;
b;
(double) a;
Functional notation
b = double (a);
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Using keyword static_cast
b = static_cast<double>(a);
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Enumerated Data Types
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
Enable to create new types and then define variables of these types
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Syntax rule
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Write the keyword enum followed by new type name
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List legal values separated by a comma within braces
enum COLOR { RED, BLUE, GREEN, WHITE, BLACK };
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Enumerated Data Types (cont.)
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
Every enumerated constant has an integer value
enum COLOR { RED=100, BLUE, GREEN=500, WHITE, BLACK=700 };
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If you don’t specify integer values, the first constant has the value 0, and the
rest count up from there

Variable declaration and manipulation
COLOR dress;
dress = RED;
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Enumerated Data Types (cont.)
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
Every enumerated constant has an integer value
enum Day { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY };
In memory...
MONDAY = 0
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TUESDAY = 1 WEDNESDAY = 2 ..etc
Using the Day declaration, the following code...
Day d = FRIDAY ;
cout << MONDAY << " " << WEDNESDAY << " " << d << endl;
..will produce this output: 0 2 4
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Enumerated Data Types (cont.)
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
You can NOT directly assign an integer value to an enum variable
Day workDay ;
workDay = 3;
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// Error!
Instead, you must cast the integer:
workDay = static_cast<Day>(3);
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You CAN assign an enumerator to an int variable
int x;
x = THURSDAY;
x = workDay ;
.. What is the value of x in each statements above?
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Exercise - 1
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1.
Write a program that declares two constant A and B
2.
Initialize A =1 and B=2.2
3.
Declare an int named C and float named D
4.
Initialize C =A and D=B
5.
Write statements to print C and D to screen
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End
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