do-while loop

Now we know about for, while loop that executed the statement within them finite number of times. However, in real life programming, one comes across a situation when it is not known beforehand how many times the statement in the loop are to be executed. In this situation we used do-while loop.

do-while tests the condition after having executed the statement within the loop i.e. do-while would executed its statement at least once, even if the condition fails for the first time. For example notice in following program:

/*demonstration of do-while*/

#include<stdio.h>

#include<conio.h>

void main()

{

 clrscr();

 do

 {

  printf("Its work!!");

 }while(10<1);

 getch();

}

Output of above program:

Its work!!

In above program, the printf() would be executed once, since first the body of loop is executed and then the condition tested, 10<1 condition false so loop terminate and go to next statement.

/*program to find factorial value of any number, and it is execute unknown number of times when user enter no, then program should be terminate.*/

#include<stdio.h>

#include<conio.h>

void main()

{

 int n,f=1;

 char choice;

 clrscr();

 do

 {

  printf("Enter number : ");

  scanf("%d",&n);

  while(n>=1)

  {

   f=f*n;

   n--;

  }

  printf("Factroial value of %d is %d",n,f);

  printf("\nCalculate another value y/n :");

  scanf("%c",&choice);

 }while(choice=='y');

}

output of above program:

Enter number :5

Factorial value of 5 is 120

Calculate another value y/n :y

Enter number :4

Factorial value of 4 is24

Calculate another value y/n :n

In above program, the do-while loop would keep getting executed till the user continues to answer y. When user enter answer n,the loop terminate, since the condition fails.