C Program to Calculate the Sum of First N Natural Numbers

Write a C program to calculate the sum of first n natural numbers. Given an input n, We have to write a code to print the sum of first n natural number (1 to n).

There are multiple approaches to solve this problem.

* We can solve this problem using loop.
* Other approach is to use mathematical formula to calculate the sum of first n natural number.
* We can also use recursion to find the sum of first n natural numbers using recursion.

Suppose if user has entered a number 10. So, we have to calculate the sum of first 10 numbers ( 1 to 10). The Sum of first 10 numbers is 55.

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How to Calculate the Sum of first N Natural Numbers

1. First approach is to use for loop to calculate the sum of first n natural numbers.

  for(i=1; i<=num; i++){

      sum +=i;
  }

 
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2. Another approach is to use mathematical formula n(n+1)/2 to calculate the sum of first n natural numbers.

Suppose, If user has entered the value of n is 20 = 20 * (20 + 1)/2 = 210

The sum of first 20 numbers is 210.

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C Program to Calculate the Sum of First n Natural Numbers using Mathematical Formula

We have discussed multiple approaches to calculate the sum of first n natural numbers. Let's write a code to solve this problem using discussed approaches.

In this approach, we are calculating the sum of first n natural numbers using mathematical formula.

#include <stdio.h>

int main()
{

    int n,sum;

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

    sum = (n*(n+1))/2;

    printf("The sum of n number is %d",sum);
    
    return 0;

}

C Program to Calculate Sum of First n Natural Numbers using For Loop

#include <stdio.h>

int main(void) {
 
 
    int n,sum=0,i;

    printf("Enter the value of n");
    scanf("%d",&n);
    
    /* Iterate from 1 to n . */

    for(i=1; i<=n; i++) {
     
     sum = sum + i;
    }
    
    printf("The sum of n number is %d",sum);
    
    return 0;
}

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Output:

Enter the value of n : 10

The sum of n number is : 55



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