Added code to free memory

stack.c

@@ -35,6 +35,7 @@ void stack_push(Stack* stack,void* element) {
 
 void* stack_pop(Stack* stack) {
 	assert( !(stack_isEmpty(stack)) );
+	free(stack->data + stack->top_index);
 	stack->top_index--;
 	void* to_return = *(stack->data + stack->top_index);
 	*(stack->data + stack->top_index) = NULL;