Do WHILE LOOP in C Programming Examples

Before understanding the programming examples of the Do-While loop, we have to know what is Do-While loop in C. So, let's start with the definition of the Do-While loop.

What is Do-while Loop?

The Do-While loop executes the body at least one time before checking the termination condition and then executes the statements according to the termination condition.

Syntax of the do-while loop in C

do 
{
  /* main body used for the loop */
}
while (termination condition);

Initially, the body of do-while executes only one time. After that, the control executes the termination condition.

It then checks whether the termination command results in true. If yes, it will print the desired outcome on the screen, and it will continue to execute the termination condition repeatedly.

One more thing is that the execution will run multiple times until the condition become false.

As soon as the results become false after the execution of the termination command, then the loop will be automatically dismissed.

Example 01: Program to perform basic addition of various numbers until the user enters 0.

/* code for adding integers until the user assigns the value zero */
#include <stdio.h>
int main() 
{
  double number, total = 0; // variable declaration and initialization of values of                                                    variables
  do 
  {
    printf("Enter a number: "); // body of “do while” loop
    scanf("%lf", &number);     // it is executed only once
    total += number; 
  }
  while(number != 0.0); // termination condition
  printf("Sum = %.2lf",total); // command for printing output 
  return 0;
}

Output

Enter a number: 3
Enter a number: 4
Enter a number: -5
Enter a number: 6
Enter a number: 0
Sum = 8.00

Step by step explanation:

In the above code, the do-while loop is used in such a manner that it lets the user enter the numbers, and the loop will be executed as long as the user does not insert a 0 integer.

The loop in this code executes the body once without checking the termination statement, so it will execute the statement first. After that, the user entered 3, 4, -5, and then 6.

At last, the user enters 0, and the "do while" loop is terminated because the termination condition becomes false. As a result, the output (the sum of all inserted numbers) is displayed on the screen.

A few more similar examples of the "do while" loop in C are discussed below.

Example 02:  Do-While loop with increment statement:

/* this is a program to print numbers to a specific point */
#include <stdio.h>
int main() 
{
  int a;
      printf("enter the number (less than or equal to 3) to start from:\n");
      scanf("%d",&a); // assigning the value entered to a
    do //execute the task without checking the condition only once
  {
      printf("the value of a is %d\n",a);
      a++;//increment statement
  }  
    while(a<=3);//this is termination condition
  return 0;
}

Output:

enter the number (less than or equal to 3) to start from:
-3
the value of a is -3
the value of a is -2
the value of a is -1
the value of a is 0
the value of a is 1
the value of a is 2
the value of a is 3

In this example, firstly, we have declared the variable "a," and then we took the input from the user and assigned the inserted value to “a”.

The code will print the value of “a” without checking the termination condition. Then, it will increment the value of “a” and check the termination condition repeatedly.

According to the input provided by the user in the mentioned output, the value of “a” is -3, but after increment, it becomes -2, -1, 0. The value will increment until ‘a’ reaches 3. When the value of 'a' becomes 3, then the loop will be terminated because the termination condition (a<=3) becomes false.

Example 03: Do-While loop with decrement statement:

/* this is a program to print numbers to a specific point */
#include <stdio.h>
int main() 
{
  int a;
      printf("enter the number (more than or equal to 3) to start from:\n");
      scanf("%d", &a); // assigning the value entered to a
    do //execute the task without checking the condition only once
  {
      printf ("the value of a is %d\n", a);
      a--; //decrement statement
  }  
    while(a>=3); //this is termination condition
  return 0;
}

Output:

enter the number (more than or equal to 3) to start from:
9
the value of a is 9
the value of a is 8
the value of a is 7
the value of a is 6
the value of a is 5
the value of a is 4 
the value of a is 3 

In this example, firstly, we declared the variable "a", then we took the input from the user and assigned the inserted value to “a”.

The code will print the value of “a” without checking the termination condition. Then, it will decrease the value of "a" and repeatedly check the termination condition.

According to the input provided by the user in the mentioned output, the value of “a” is 9, but after decrement, it becomes 8, 7, and 6. The value will decrement until ‘a’ reaches 3. When the value of 'a' becomes 3, then the loop will be terminated because the termination condition (a>=3) becomes false.

Example 04: Program of Do-While loop:

/* this program will calculate the sum of all multiples of the table */
#include <stdio.h>
int main() 
{
  int num , sum, a=0; // Declaring variables and initialization of the value of a
      printf("enter the table you want to add:\n\n");
      scanf("%d", &num);//assigning the value of a entered by user
    do
  {
      printf("%d * %d = %d \n\n", num, a, num * a);
      a++;// increment statement
  }
    while(a<=10);// termination condition
      sum=num*55;
  {
      printf("the sum of all multiples of this table is %d\n\n", sum);
  }
    return 0;
}

Output:

enter the table you want to add:
8
8 * 0 = 0 
8 * 1 = 8
8 * 2 = 16
8 * 3 = 24
8 * 4 = 32
8 * 5 = 40
8 * 6 = 48
8 * 7 = 56
8 * 8 = 64
8 * 9 = 72
8 * 10 = 80
the sum of all multiples of this table is 440

the sum of all multiples of this table is 440

Example 05: Do-While loop with positive infinity:

/* this is a program to print numbers to an uncertain point */
#include <stdio.h>
int main() 
{
  int a;// declaring variable
      printf("enter the number (more than or equal to 3) to start from:\n");
      scanf("%d", &a); // assigning the value entered to a
    do //execute the task without checking the condition only once
  {
      printf ("the value of a is %d\n", a);
      a++; //increment statement
  }  
    while(a>=3); //this is termination condition
  return 0;
}

Output:

enter the number (more than or equal to 3) to start from:
3
the value of a is 4
the value of a is 5
the value of a is 6
the value of a is 7
the value of a is 8
the value of a is 9 
the value of a is 10………

Example 06: Do-While loop with negative infinity:

/* this is a program to print numbers to an unspecified point */
#include <stdio.h>
int main() 
{
  int a; //declaring variable
      printf("enter the number (less than or equal to 3) to start from:\n");
      scanf("%d", &a); // assigning the value entered to a
    do //execute the task once without checking the condition
  {
      printf ("the value of a is %d\n", a);
      a--; //decrement statement
  }  
    while(a<=3); //this is termination condition
  return 0;
}

Output:

enter the number (less than or equal to 3) to start from:
3
the value of a is 2
the value of a is 1
the value of a is 0
the value of a is -1
the value of a is -2
the value of a is -3
the value of a is -4………….