7(iii)

#include <stdio.h>
int sum(int);
int main()
{
    int num;
    printf("Enter the Number: ");
    scanf("%d", &num);
    printf("Sum = %d", sum(num));
    return 0;
}

int sum(int n)
{
    if (n == 0)
        return 0;
    else
        return n + sum(n - 1);
}