C Program to find sum of n natural numbers using recursion

Program

#include<stdio.h>
int sum(int);
void main()
{
	int n, sum;
	printf("Enter the value of n:\t");
	scanf("%d", &n);
	sum = sum_rec(n);
	printf("Sum of %d numbers: %d\n", n, sum);
}
int sum_rec(int num)
{
	int res;
	if (num == 1)
		return 1;
	else
		res = num + sum_rec(num - 1);
	return res;
}

Output

Enter the value of n:	12
Sum of 12 numbers: 78