Подскажите где ошибка?

#include <iostream>
using namespace std;

const int Max_size=1000;

class stack{
private:
	int s_size;
	int mass[Max_size];
public:
	stack();
	~stack();
	void push(int e);
	int pop();
	int back();
	int size();
	void clear();
};
stack::stack()
{
	s_size=0;
}
stack::~stack()
{
}
void stack::push(int e)
{
	if(s_size==Max_size)
	{
		cout<<"stek polon";
		return;
	}
	mass[s_size]=e;
	s_size++;
}
int stack::pop()
{
	if(s_size==0)
	{
		cout<<"stek pust";
		return 0;
	}
		s_size--;
		return mass[s_size];
}
int stack::back()
{
	if(s_size==0)
	{
		cout<<"stek pust";
		return 0;
	}
	
	return mass[s_size-1];
	
}
int stack::size()
{
	return s_size;
}
void stack::clear()
{
	s_size=0;
}





int main()
{
	stack stack1;
	char *t[6]={"push","pop","back","size","clear","exit"};
	char *r="";
	char *res="";
	int q,n;

do
{
	gets(r);
	for(int i=0; i<6; i++)
	{
		res=strstr(r,t[i]);
		if(res)
		{
			q=i;
			break;
		}
	}
	switch(q)
	{
	case 0:
		n=atoi(r);
		stack1.push(n);
		cout<<"ok\n";
		break;
	case 1:
		cout<<stack1.pop();
		break;
	case 2:
		cout<<stack1.back();
		break;
	case 3:
		cout<<stack1.size();
		break;
	case 4:
		stack1.clear();
		break;
	case 5:
		return 0;
	}
} while(1);

return 0;
}

 char *r = new char[10];