#include <iostream>
using namespace std;

/**
 * Definition of class A that stores an integer
 */
class A {
public:
	// value stored
	int value;
	
	/**
	 * default constructor
	 * initialization of value to -1
	 */
	A() {
		value = -1;
	}
	
	/**
	 * constructor with value
	 * @param v value to store
	 */
	A(int v) {
		value = v;
	}
	
	/**
	 * print class contents
	 */
	friend ostream& operator<<(ostream& out, A& obj) {
		out << obj.value;
		return out;
	}
};

// ----------------------------------------------
// function that will produce an error
// we are trying to exchange values
// ----------------------------------------------
int function_1(const A& x, const A& y) {
	// by default lets assume 'x' is the smallest value
	// and 'y' the biggest
	A& smallest = const_cast<A&>(x);
	A& biggest = const_cast<A&>(y);
	
	cout << "> in function:" << endl;
	cout << "smallest = " << smallest << endl;
	cout << "biggest  = " << biggest << endl;
	
	// if it is not the case then exchance 'x' and 'y'
	if (smallest.value > biggest.value) {
		// !!!!! problem here !!!!! 
		// it is equivalent to: x = y
		smallest = const_cast<A&>(y);
		 
		biggest = const_cast<A&>(x);
		cout << "> in function after exchange:" << endl;
		cout << "smallest = " << smallest << endl;
		cout << "biggest  = " << biggest << endl;		
	}
	
	return (biggest.value - smallest.value);
}

// ----------------------------------------------
// valid function 
// we are trying to exchange values
// ----------------------------------------------
int function_2(const A& x, const A& y) {
	// work on values not references
	int smallest = x.value;
	int biggest  = y.value;
	
	cout << "> in function:" << endl;
	cout << "smallest = " << smallest << endl;
	cout << "biggest  = " << biggest << endl;
	
	if (smallest > biggest) {
		swap(smallest, biggest);
	}
	
	return (biggest - smallest);
}


// ----------------------------------------------
// main function
// ----------------------------------------------
int main() {
	A a1(7), a2(5);


	cout << "==== with function_1 ====" << endl;
	cout << "initially :" << endl;
	cout << "a1 = " << a1 << endl;
	cout << "a2 = " << a2 << endl;
	
	int r = function_1(a1, a2);
	cout << "r = " << r << endl;
	
	// !!! a1 is modified after call to function !!!
	cout << "finally :" << endl;
	cout << "a1 = " << a1 << " !!! should be 7" << endl;
	cout << "a2 = " << a2 << endl;

	cout << "==== with function_2 ====" << endl;
	A b1(7), b2(5);
	cout << "initially :" << endl;
	cout << "b1 = " << b1 << endl;
	cout << "b2 = " << b2 << endl;
	
	r = function_2(b1, b2);
	cout << "r = " << r << endl;
	
	cout << "finally :" << endl;
	cout << "b1 = " << b1 << endl;
	cout << "b2 = " << b2 << endl;
	
	return 0;
}