struct Token {
	char kind;
	double value;
	string name;
	Token(char ch) :kind(ch), value(0) { }
	Token(char ch, double val) :kind(ch), value(val) { }
	Token(char ch, string n) :kind(ch), name(n) {}
};

class Token_stream {
	bool full;     
	Token buffer;  
public:
	Token_stream() :full(0), buffer(0) { }         

	Token get();                                  
	void unget(Token t) { buffer=t; full=true; }  

	void ignore(char c);       
};

double term()
{
	double left = primary();
	Token t = ts.get();  

	while(true) {
		switch(t.kind) {
		case '*':
			left *= primary();
			t = ts.get();
			break;
		case '/':
		{	double d = primary();
			if (d == 0) error("divide by zero");
			left /= d;
			t = ts.get();
			break;
		}
		case '%':
			{ double d = primary();
			  int i1 = int(left);
			  if (i1 != left) error ("left operand of % is not an integer");
			  int i2 = int(d);
			  if (i2 != d) error ("right operand of % is not an integer");
			  if (i2 == 0) error ("% divide by zero");
			  left = i1 % i2;
			  t = ts.get();
			  break;
			}
		case 'S':
			{
			  double d = primary();
			  if (d < 0) error("no negative square root calculations");
			  if (d > 0) left = sqrt(d);
			  t = ts.get();
			  break;
			}  
		default:
			ts.unget(t);  
			return left;
		}
	}
}

void calculate()
{
	cout<<">This is a calculator program. This can calculate with '+,-,*,/,%' only!\n";
	cout<<">For result press '=' and to end the program press 'q'!\n";
	while(cin) try {        
		cout << prompt;
		Token t = ts.get();
		while (t.kind == print) t=ts.get();    
		if (t.kind == quit) return;            
		ts.unget(t);
		cout << result << statement() << endl;
	}
	catch(runtime_error& e) {
		cerr << e.what() << endl;              
		clean_up_mess();
	}
}

int main()

	try {
		calculate();
		keep_window_open();     
		return 0;
	}
	catch (exception& e) {      
		cerr << e.what() << endl;
		keep_window_open("~~");
		return 1;
	}
	catch (...) {
		cerr << "exception\n";
		keep_window_open("~~");
		return 2;
	}

double d = narrow_cast<double>(left);