C Program to find the Sum of First n Natural numbers

June 5, 2021

Program to find the sum of first n natural numbers. We will see two C programs to calculate the sum of natural numbers. In the first C program we are using for loop for find the sum and in the second program we are doing the same using while loop.
To understand these programs, you should be familiar with the following C Programming Concepts:

  1. C Programming for loop
  2. C Programming while loop

Example 1: Program to find sum of natural numbers using for loop

The user enters the value of n and the program calculate the sum of first n natural numbers using for loop.

#include <stdio.h>
int main()
{
    int n, count, sum = 0;

    printf("Enter the value of n(positive integer): ");
    scanf("%d",&n);

    for(count=1; count <= n; count++)
    {
        sum = sum + count;
    }

    printf("Sum of first %d natural numbers is: %d",n, sum);

    return 0;
}

Output:

Enter the value of n(positive integer): 6
Sum of first 6 natural numbers is: 21

Example 2: Find the sum of natural numbers using while loop

#include <stdio.h>
int main()
{
    int n, count, sum = 0;

    printf("Enter the value of n(positive integer): ");
    scanf("%d",&n);

    /* When you use while loop, you have to initialize the
     * loop counter variable before the loop and increment
     * or decrement it inside the body of loop like we did 
     * for the variable "count"
     */
    count=1;
    while(count <= n){
    	sum = sum + count;
    	count++;
    }

    printf("Sum of first %d natural numbers is: %d",n, sum);

    return 0;
}

Output:

Enter the value of n(positive integer): 7
Sum of first 7 natural numbers is: 28

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