#include <assert.h>

class Istack {
	int sz;
	int top;
	int* stack;
public:
	void init(int Nitems = 100) { sz = Nitems; 
					stack = new int[sz]; top = sz; }
	void push(int x) { assert( !isfull() ); 
								stack[--top] = x; }
	int pop() { assert( !isempty() ); 
						return( stack[top++] ); }
	bool isempty() { return(( top == sz )); }
	bool isfull() { return(( top == 0)); }
};
class Cstack { 	// Changed
	int sz;
	int top;
	char* stack; 		// Changed
public:
	// init, push, and pop are changed
	void init(int Nitems = 100) { sz = Nitems; 
				stack = new char[sz]; top = sz; }
	void push(char x) { assert( !isfull() ); 
								stack[--top] = x; }
	char pop() { assert( !isempty() ); 
						return( stack[top++] ); }
	bool isempty() { return(( top == sz )); }
	bool isfull() { return(( top == 0)); }
};