# C Program to find the sum of natural numbers upto N terms

Last updated on September 23, 2020

## What are Natural numbers? #

Integers used for counting are known as natural numbers. Natural numbers start with 1 and goes on to infinity. For example:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10 . . .


The following is a C program to calculate the sum of natural numbers upto n terms:

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 /********************************************************** * Program to find the sum of natural numbers upto n terms ***********************************************************/ #include // include stdio.h int main() { int terms, i; unsigned long int sum = 0; printf("Enter the number of terms: "); scanf("%d", &terms); for(int i = 1 ; i <= terms; i++) { sum += i; } printf("%ld", sum); return 0; } 

Expected Output:

1st run:

 1 2 Enter the number of terms: 4 10 

2nd run:

 1 2 Enter the number of terms: 50000 1250025000 

## How it works#

The following table demonstrates what happens at each iteration of the for loop, assuming terms = 4.

Iteration sum i
After 1st iteration sum = sum + i = 0+1 = 1 i = 2
After 2nd iteration sum = 1+2 = 3 i = 3
After 3rd iteration sum = 3+3 = 6 i = 4
After 4th iteration sum = 6+4 = 10 i = 5`