Find the Sum of Natural Numbers using Recursion

The positive numbers 1, 2, 3... are known as natural numbers.The program below takes a positive integer from the user and calculates the sum up to that number.

Example: Sum of Natural Numbers Using Recursion

#include <stdio.h>
int addNumbers(int n);

int main()
{
    int n;
    printf("Enter a positive integer: ");
    scanf("%d", &n);
    printf("Sum = %d",addNumbers(n));
    return 0;
}
int addNumbers(int n)
{
    if(n!=0)
        return n+addNumbers(n-1);
    else
        return n;
}

Output

Enter a positive integer: 20
Sum = 210

Suppose the user entered 20.

Initially, the addNumbers() is called from the main() function with 20 passed as an argument.

In the next function call from addNumbers() to addNumbers(), 19 is passed. Then, 18 is passed to the function. This process continues until n is equal to 0.

When n is equal to 0, there is no recursive call and the sum of integers is returned to the main() function.