Information Hiding -- The Problem of Stacks

int datastack[100];
int datatop = 0;

void init()     // initialize the stack
{ datatop = 0; }

void push(int val)   // push a value on to the stack
{ if (datatop < 100)
		datastack [datatop++] = val; }

int top()   // get the top of the stack
{ if (datatop > 0)
		return datastack [datatop - 1];
	return 0; }

int pop()   // pop element from the stack
{ if (datatop > 0)
		return datastack [--datatop]; 
	return 0; }