#include <cstdlib>
#include <iostream>
#include <exception>

class invalid_expr : public std::exception {
public:
    virtual const char* what() const noexcept {
	return "this expression is bad!";
    }
private:
    int i;
};

void abandon_ship() {
    std::cout << "Mayday mayday mayday!" << std::endl;
    std::exit(0);
}

int eval(int expr) throw (int) {
    // normal, VALID case
    if (expr > 7)
	return expr - 3;
    // absnormal, INVALID case
    if (expr < 0) {
	invalid_expr e;
	throw e;
    }
    switch (expr) {
    case 0: throw(0); // small error
    case 1: throw(1); // big error;
    case 2: throw("huge error");
    default: throw("nasty error!"); 
    }
}

void read_integer(int & i) {
    std::cout << "Input: ";
    std::cin >> i;
}

int main() {
    std::set_unexpected(abandon_ship);

    try {
	int i;
	read_integer(i);
	std::cout << "OUTPUT: ";
	std::cout << eval(i) << std::endl;
    } catch (int ex) {
	std::cout << "error number " << ex << std::endl;
    } catch (const char * error_msg) {
	std::cout << error_msg << std::endl;
    } catch (const std::exception & e) {
	std::cout << "Check out this exception: " << e.what() << std::endl;
    }
}