typedef struct stack *Stack;

/** Creates a new empty stack */
Stack StackNew(void);

/** Frees memory allocated to the stack */
void StackFree(Stack s);

/** Adds an item to the top of the stack */
void StackPush(Stack s, int item);

/** Removes the item at the top of the stack
Assumes that the stack is not empty */
int StackPop(Stack s);