Do-While Loop with Example in C: Computer Programming

In Computer programming, do-while loop is similar to while loop and used when a set of statements may have to be repeatedly executed until a certain condition is reached. When we do not know exactly how many times a set of statements have to be repeated, do-while can be used. The syntax of the do-while loop is shown below in C:

do
{
 statement1;
 statement2;
 statement3;
   .
   .
statementn;
} while (exp);

Where

• do and while – are reserve words or keywords
• exp – is the expression which is evaluated to TRUE or FALSE. The semicolon indicates the termination of the loop.

Working of do-while loop:
The following sequences of the operations are carried out during the execution of the do-while loop statement:

• The body of the do-while loop consisting of statements statement-1, statement-2,….statement-n are executed.
• Then, the exp is evaluated. If the expression exp is evaluated to TRUE, the body of the loop is executed again and the process is repeated.
• If the exp is evaluated to FALSE, control comes out of the do-while loop and the statements after (outside) the do-while loop are executed.

Since the expression exp is evaluated to TRUE or FALSE at the bottom of the do-while loop, so, the do-while loop is called bottom testing loop or exit controlled loop. Here, the body of the loop is executed at least once.

Difference between while & do-while loop

Here's an example to get sum of 1 to given no.s
Algorithm:

Step1:    [Input the number of terms]
    Read: n
Step2:    [Initialization]
    sum=0
    i=0
Step3:    do
    sum = sum+i
    i = i+1
    while (i<=n)
Step4:    Write: sum
Step5:    Exit

C program
main()
{
int n,i,sum;
clrscr();
printf("Enter the value of n here: \n");
scanf("%d",&n);
sum=i=0;
do
{
sum=sum+i;
i++;
}while(i<=n);

printf("Sum of the series is %d",sum);
getch();
}

Read Also: Jump statements in C