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

	/*
	 *  malloc() takes one argument: # of bytes to allocate
	 *  # of bytes will equal, (# of elements) * (sizeof(data type))
	 *  If creating an integer array with 10 elements, use:
	 *  malloc( 10 * sizeof(int) )
	 *  NOTE: malloc() will return a pointer to the head
	 *  of this newly allocated memory
	 *
	 *  ADDITIONAL NOTE: malloc() will NOT initialize any element of the array
	 *  All elements of array are garbage values until values are manually assigned
	 */

	int main(void) {

		// int * arr will store a pointer to an integer array of size arrLen
		// NOTE: adding (int*) explicitly casts malloc to integer pointer
		// HOWEVER - without (int*) in front, cast is implicit / still works
		int arrLen = 20;
		int *arr = (int *)malloc(arrLen * sizeof(int));

		// Initializes each element of array to zero
		for (int i = 0; i < arrLen; i++)
			arr[i] = 0;

		/////////////////////////////////////////////////////////////////////////////

		// malloc() for strings
		// Strings end with a NULL terminator ('\0')
		// String memory must be allocated as string length + 1 to create additional
		// space for NULL terminator
		char str[] = "puppy";
		int len = strlen(str);

		// To copy statically allocated string str to a dynamically allocated variable
		// First, the appropriate space must be allocated
		// NOTE: (len + 1) for NULL terminator
		char *newStr = malloc((len + 1) * sizeof(char));

		// Once memory is allocated, string can be copied using strcpy()
		strcpy(newStr, str);

		/////////////////////////////////////////////////////////////////////////////

		// pointer to pointer [In this example being used as a 2D array]
		// A pointer to pointer can create an array of pointers
		// Each element in the array can point to its own array
		// NOTE: Cast to (int**) but each element is sizeof(int*)
		int numElements = 10;
		int **arr2D = (int **)malloc(numElements * sizeof(int *));

		// Now that array of pointers is allocated, each element points to garbage
		// These pointers can be manually set
		int sizeEachElement = 5;

		// Initializes each element of array to zero
		for (int i = 0; i < numElements; i++) {

			// First allocate space
			arr2D[i] = (int *)malloc(sizeEachElement * sizeof(int));

			// Then initialize each element
			for (int j = 0; j < sizeEachElement; j++) {
				arr2D[i][j] = 0;
			}
		}

		/////////////////////////////////////////////////////////////////////////////

		// Always free dynamically allocated memory when you're done with it
		for (int i = 0; i < numElements; i++) {
			free(arr2D[i]);
		}
		free(arr2D);
		free(newStr);
		free(arr);

		printf("I hope this has helped to teach you how malloc() works :)\n");

		return 0;
	}