/****************************************************************************
 * sigma2.c
 *
 * David J. Malan
 * malan@harvard.edu
 *
 * Adds the numbers 1 through n.
 *
 * Demonstrates recursion.
 ***************************************************************************/

#include <cs50.h>
#include <stdio.h>

// prototype
int sigma(int);

int main(void)
{
    // ask user for a positive int
    int n;
    do
    {
        printf("Positive integer please: ");
        n = GetInt();
    }
    while (n < 1);

    // compute sum of 1 through n
    int answer = sigma(n);

    // report answer
    printf("%d\n", answer);

    return 0;
}

/**
 * Returns sum of 1 through m; returns 0 if m is not positive.
 */
int sigma(int m)
{
    // base case
    if (m <= 0)
        return 0;

    // recursive case
    else
        return (m + sigma(m-1));
}