C - do while loop in C programming

For video tutorial you can see below video:- 

👉A do while loop is similar to while loop with one exception that it executes the statements inside the body of do-while before checking the condition.

👉On the other hand in the while loop, first the condition is checked and then the statements in while loop are executed. 

👉So you can say that if a condition is false at the first place then the do while would run once, however the while loop would not run at all.

👉A do...while loop is similar to a while loop, except the fact that it is guaranteed to execute at least one time.

Syntax:

The syntax of a do...while loop in C programming language is :-

do {

   statement(s);

} while( condition );

👉Notice that the conditional expression appears at the end of the loop, so the statement(s) in the loop executes once before the condition is tested.

👉If the condition is true, the flow of control jumps back up to do, and the statement(s) in the loop executes again. This process repeats until the given condition becomes false.

Flow Diagram:

How does a do-While loop executes?

✔    Control falls into the do-while loop.

✔    The statements inside the body of the loop get executed.

✔    Updation takes place.

✔    The flow jumps to Condition

✔    Condition is tested.

⭐    If Condition yields true, goto Step 6.

⭐    If Condition yields false, the flow goes outside the loop

✔    Flow goes back to Step 2.

The following program illustrates the working of a do-while loop:

      ⭐We are going to print a table of number 2 using do while loop.

#include<stdio.h>

#include<conio.h>

void main()

{

         int num=1;       //initializing the variable

         clrscr();

         do       //do-while loop

         {

                 printf("%d\n",2*num);

                 num++;           //incrementing operation

         }while(num<=10);

         getch();

}

Output:

2

4

6

8

10

12

14

16

18

20

👉In the above example, we have printed multiplication table of 2 using a do-while loop. Let's see how the program was able to print the series.

✔   First, we have initialized a variable 'num' with value 1. Then we have written a do-while loop.

✔   In a loop, we have a print function that will print the series by multiplying the value of num with 2.

✔   After each increment, the value of num will increase by 1, and it will be printed on the screen.

✔   Initially, the value of num is 1. In a body of a loop, the print function will be executed in this way: 2*num where num=1, then 2*1=2 hence the value two will be printed. This will go on until the value of num becomes 10. After that loop will be terminated and a statement which is immediately after the loop will be executed. In this case return 0.