/**
 * Variables must be explicitly allocated and
 * explicitly freed. All dereference must be 
 * explicit.
 * If you want to allocate memory inside a function and return
 * it to the calling function, then you need to allocate that memory
 * on the heap (malloc!).
 */

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

int* createThing( ) {
    int thing = 10;
    return &thing; // Don't do this!!! The memory that was allocated on the call stack will be gone.
}

int main (int argc, char* arvg[]) {
	int *a = (int *)malloc(sizeof(int));
	
	*a = 4;
	printf( "a has a value that is an address: %p\n", a );
	printf( "*a =%d\n", *a );
	
	free(a);	
// 	printf( "a has a value that is an address: %p\n", a ); // Don't do this! You no longer have the right to look at that address.
// 	printf( "*a =%d\n", *a );
	
	a = createThing();
	printf( "a has a value that is an address: %p\n", a );
	printf( "*a =%d\n", *a );
	
	// dereferencing a NULL pointer leads to a segmentation fault.
	int *b = NULL;
	printf( "*b = %d\n", *b );
	
	return(0);
}