/****************************************************************************
 * 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(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);
}


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

int
sigma(int m)
{
    // avoid risk of infinite loop
    if (m < 1)
        return 0;

    // return sum of 1 through m
    int sum = 0;
    for (int i = 1; i <= m; i++)
        sum += i;
    return sum;
}