//This program gives an example of how you can allocate memory
//for an array and then read in the array and print it out in 
//reverse order.

//Sasha Vassar Week 7 Lecture 11

#include <stdio.h>
//malloc() and free() live inside the <stdlib.h>
#include <stdlib.h>

void read_array(int *numbers, int size);
void reverse_array(int *numbers, int size);

int main (void) {
    
    int size;
    printf("How many numbers would you like to scan: ");
    scanf("%d", &size);
    
    //TODO: Allocate some memory space for my array and return a pointer
    //to the first element
    //Malloc is the function that allocates memory
    // Malloc returns a pointer to the allocated memory
    // Malloc takes in the number of bytes needed
    int *numbers = malloc(size * sizeof(int));
    // 5 numbers  = 5 * 4 = 20 bytes  
    // A pointer can point to NULL, which means it is poitning to nothing! 
    // if there is not enough memory that malloc needs, it will return a NULL 
    
    //TODO: Check if there is actually enough space to allocate
    //memory, exit the program if there is not enough memory
    //to allocate.
    if (numbers == NULL) {
        printf("Error, malloc failed, there is not enough space to allocate\n");
        return 1;
    }
    
    //Perform some functions here  
    read_array(numbers, size);
    reverse_array(numbers, size);
  
    //Free the allocated memory
    //In this case, it would happen on program exit anyway
    free(numbers);
    return 0;
}

//Helper function that reads in numbers and places them into an array
//Inputs are the pointer to the first element of the array, and the size of 
//the array. 
void read_array(int *numbers, int size){
    int i = 0;
    while (i < size) {
        printf("Enter a number to scan in: ");
        scanf("%d", &numbers[i]);
        i++;
    }
}

//TODO: Finish the helper function to reverse the elements of the array
void reverse_array(int *numbers, int size){
    printf("Numbers reversed are:\n");
    int last = size - 1;
    while (last >= 0) {
        printf("%d\n", numbers[last]);
        last--;
    }
}