/*
 * heap.c
 *
 * Computer Science 50, Fall 2011
 * section4
 *
 * Working with variables created in the heap.
 */

#include <stdio.h>
#include <stdlib.h>

// functions prototypes
int* f();
int* g();

int
main(void)
{
    // creates a pointer to a variable created in f()
    int* x = f();

    printf("x has the value %d\n", *x);

    // creates a pointer to a variable created in f()    
    int* y = g();
    
    printf("x (still) has the value %d\n", *x);
    printf("y has the value %d\n", *y);

    // always remember to do this!
    free(x);
    free(y);
}

int*
f()
{
    // declares a pointer
    int* a;
    
    // reserves some space in the heap
    do
    {
        // sets 'a' equal to the address of the reserved space 
        a = malloc(sizeof(int));
    } while(a == NULL); // goes until we're sure we got some space

    // sets the space 'a' points to equal to 5
    *a = 5;
    
    // returns the value of a (i.e. the address of the space in the heap)
    return a;
}

int*
g()
{
    // see comments in f()
    int* b;
    
    do
    {
        b = malloc(sizeof(int));
    } while(b == NULL);
    
    *b = 10;
    return b;
}