/**
 * @file sum.c
 * @brief Example of sums using with function prototypes.
 *
 * This file contains three sum functions showing basic functionality. It also
 * uses forward declarations, separating the declaration and the definition of
 * the "sum" functions. Note how the functions are declared above main() and
 * defined below main.
 *
 * @author Michael J. Bannister
 * @author Peter Mawhorter
 * @date 10 Nov 2015
 * @date 10 Nov 2016
 */
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>

// Forward declaration of functions.
// Functions need to be declared before their first use.
int sum_one(int n);
int sum_two(int n);
int sum_three(int n);

// Program entry point.
int main() {
    fputs("Please enter a number: ", stdout);
    int n = 0;
    fscanf(stdin, "%d", &n);

    fprintf(
      stdout,
      "The sum of the number from 1 to %d is %d.\n",
      n,
      sum_one(n)
    );
    fprintf(
      stdout,
      "The sum of the number from 1 to %d is %d.\n",
      n,
      sum_two(n)
    );
    fprintf(
      stdout,
      "The sum of the number from 1 to %d is %d.\n",
      n,
      sum_three(n)
    );

    return EXIT_SUCCESS;
}

// Function definitions below this point.
// Functions are defined here after they are used.
int sum_one(int n) {
    assert(n > 0);
    int sum = 0;
    for (int i = 1; i <= n; i++) {
        sum += i;
    }
    return sum;
}

int sum_two(int n) {
    assert(n > 0);
    int A[n];
    for (int i = 0; i < n; i++) {
        A[i] = i + 1;
    }
    int sum = 0;
    for (int i = 0; i < n; i++) {
        sum += A[i];
    }
    return sum;
}

int sum_three(int n) {
    assert(n > 0);
    if (n == 1) {
        return 1;
    }

    return n + sum_three(n - 1);
}