Computer Programming -1Lecture 8
Iteration Statements
 There may be a situation, when you need to execute a block of code
several number of times. In general statements are executed sequentially:
The first statement in a function is executed first, followed by the second,
and so on.
 Programming languages provide various control structures that allow for
more complicated execution paths.
 Iteration Statements :
 for loop
 while loop
 do-while loop
The for statement (for loop)
The For Loop Statement : is an iteration statement that executes a set of
code repeatedly, given the initial value, the condition ,increment or
decrement value.
The for statement (for loop)
The syntax of a for loop in C++ is:
for(initialization ; condition ; increase or decrease)
{
statement;
}
Example :
For ( int i=1 ; i<=10 ; i++)
cout << " * “ ;
Output : **********
Examples :
* Print numbers from 1 to 20 :
for ( int j=1 ; j<=20 ; j++)
cout << j << "\t" ;
Output : 1 2 3 4 5 …………….. 20
* Print numbers from 20 to 1 :
for ( int j=20 ; j>=1 ; j--)
cout << j << "\t" ;
Output : 20 19 18 17 …………….. 1
* Even number :
for ( int i=2 ; i<=20 ; i+=2 )
cout << i << "\t" ;
Output : 2 4 6 8 10 …………….. 20
* Odd number :
for ( int i=1 ; i<=20 ; i+=2)
cout << i << "\t" ;
Output : 1 3 5 7 9 …………….. 19
- Write a C++ program by using for statement to print only
odd numbers from 1 to 100
#include <iostream.h>
int main ()
{
for ( int i=1 ; i<100 ; i+=2 )
cout << i << endl ;
return 0 ;
}
- Write a C++ program by using for statement to print
characters from A to Z
#include <iostream.h>
int main ()
{
for ( char i='A' ; i<='Z' ; i++ )
cout << i << " , " ;
return 0 ;
}
- Write a C++ program by using for statement to print the
Even numbers from 0 to (n) numbers.
#include <iostream.h>
int main()
{
int n;
cout<<"Enter the number : ";
cin>>n;
for (int i=0 ; i<=n ; i+=2 )
cout << i << "\t";
return 0;
}
- Write a program to calculate the sum of numbers from 1
to n numbers? (n: any number enter by user )
#include <iostream.h>
int main()
{
int n;
float sum;
sum=0;
cout<<"Enter the number : ";
cin>>n;
for (int j=1 ; j<=n ; j++ )
{
sum=sum+j ;
}
cout << "the sum of numbers = "<< sum << endl;
return 0;
}
Nested for loops
Example :
#include <iostream.h>
int main()
{
for(int i=5 ; i>=1 ; i--)
{
for(int j=1 ; j<=i ; j++)
cout << " * " << " " ;
cout << endl;
}
return 0 ;
}
Output:
*****
****
***
**
*
Nested for loops
Example :
#include <iostream.h>
int main()
{
for ( int i=5 ; i>=1 ; i--)
{
for(int x=1 ; x<=5 ; x++)
cout << "*" <<" ";
cout << endl;
}
return 0 ;
}
Output :
*****
*****
*****
*****
*****
While Loop
The while loop : allows programs to repeat a statement or
series of statements, as long as a certain test condition is
true.
While Loop
The syntax of a While loop in C++ is:
initializing
while (condition)
{
statements;
increment or decrement value;
}
Example :
a=1
while (a<=10)
{
cout << " * " ;
a++;
}
Output :
**********
Examples :
* Print numbers from 1 to 10 :
int i=1;
while(i<=10)
{
cout<<i<<" ,";
i++;
}
* Print numbers from 10 to 1 :
int i=10;
while(i>=1)
{
cout<<i<<" ,";
i--;
}
- Write a C++ program by using while loop statement to print
only even numbers from 0 to 100
#include<iostream.h>
int main()
{
int i=0;
while(i<=100)
{
cout<<i<<endl;
i+=2;
}
return 0;
}
- Write a C++ program by using while loop statement to find the
sum of odd numbers from 1 to 100.
#include<iostream.h>
int main()
{
int i=1 , sum=0;
while(i<=100)
{
sum =sum + i;
i+=2;
}
cout<<" the sum is : " << sum << endl;
return 0;
}
- Write a C++ program by using while statement to find the square and
cubic values of the numbers ( the numbers is entered by user ..until the
user ask for termination )
#include<iostream.h>
int main()
{
int a;
cout << " To stop work of the program enter the number (0) " <<endl ;
while(a != 0)
{
cout << " enter the number : " ;
cin >> a ;
cout << " square = " << a*a <<endl;
cout << " cubic = " << a*a*a <<endl;
}
return 0;
}
Do while Loop
The do-while loop: is similar to the while loop, except that the
test condition occurs at the end of the loop.
The syntax of a While loop in C++ is:
do
{
statement;
increment or decrement value;
}
while(condition);
-Write a C++ program by using do while statement to print
numbers from 1 to 10
#include<iostream.h>
main()
{
int i=1;
do
{
cout<<i<<endl;
i++;
}
while(i<=10);
return 0;
}
-Write a C++ program by using do while statement to print
only even numbers from 20 to 1
#include<iostream.h>
main()
{
int i=20;
do
{
cout<<i<<endl;
i-=2;
}
while(i>=1);
return 0;
}
- Write a C++ program by using do while statement to request the user
to enter any number and exit if input is equal 6 ..
#include<iostream.h>
main()
{
int a;
do
{
cout << " enter the number : " ;
cin >> a ;
}
while(a != 6);
return 0;
}
Deciding Which Loop to Use
 while: pretest loop; loop body may not be executed
at all
 do-while: posttest loop; loop body will always be
executed at least once
 for: pretest loop with initialization and update
expression; useful with counters, or if precise number of
repetitions is needed
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Nested Loops
 A nested loop is a loop inside the body of another loop
 Inner (inside), outer (outside) loops:
for (row=1; row<=3; row++) //outer
{
for (col=1; col<=3; col++)//inner
cout << row * col <<“\t”;
cout<<endl;
}
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Lines from Program 5-16
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Nested Loops - Notes
 Inner loop goes through all repetitions for each repetition of
outer loop
 Inner loop repetitions complete sooner than outer loop
 Total number of repetitions for inner loop is product of number
of repetitions of the two loops.
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Breaking Out of a Loop
 Can use break to terminate execution of a loop
 Use sparingly if at all – makes code harder to understand and
debug
 When used in an inner loop, terminates that loop only and goes
back to outer loop
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The continue Statement
 Can use continue to go to end of loop and prepare for
next repetition
 while, do-while loops: go to test, repeat loop if test
passes
 for loop: perform update step, then test, then repeat loop if
test passes
 Use sparingly – like break, can make program logic hard
to follow
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