/****************************************************************************
 * sigma1.c
 *
 * Computer Science 50
 * David J. Malan
 *
 * Adds the numbers 1 through n.
 *
 * Demonstrates iteration.
 ***************************************************************************/
       
#include <cs50.h>
#include <stdio.h>


/* prototype */
int sigma(int);


int
main(int argc, char * argv[])
{
    int answer, n;

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

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

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


/*
 * int
 * sigma(int m)
 *
 * Returns sum of 1 through m; returns 0 if m is not positive.
 */

int
sigma(int m)
{
    int i, sum = 0;

    /* avoid risk of infinite loop */
    if (m < 1) 
        return 0;

    /* return sum of 1 through m */
    for (i = 1; i <= m; i++)
        sum += i;
    return sum;
}