Overloading(creating) operators (BCPPB 5.0)

Hello. I would like to ask you to explain or give some example of overloading operators to me. I mean something like ==. Thank you.

http://www.parashift.com/c++-faq-lit...erloading.html

Code:

struct foo
{
    int age;
    string fname;
    string lname;
};

bool operator==(const foo& lhs,const foo& rhs)
{
    return lhs.age == rhs.age && lhs.fname == rhs.fname && lhs.lname == rhs.lname;
}

Code:

#include <iostream>
#include <string>
using namespace std;

class Apple
{ 
private:
	string color;

public:
	Apple(string c)
	{
		color = c;
	}

	Apple& operator=(const Apple& rhs)  //the return value is so you can write:
                                               //apple1 = apple2 = apple3;
	{
		if(this == &rhs)  //if they are the same objects, 
                                 //no need to do any assignments
			return *this;  

		else if(rhs.color == "black") //don't do the assignment
		{
			cout<<"The Apple is rotten."<<endl;
			return *this;  
		}
		else //do the assignment
		{
			this->color = rhs.color;
			return *this;
		}




	}

	void show()
	{
		cout<<"My apple's color is: "<<color<<endl;
	}
};

int main()
{
	Apple redApple("red");
	Apple blackApple("black");
	Apple greenApple("green");
	
	redApple = greenApple;
	redApple.show();
	cout<<endl;

	greenApple = blackApple;
	greenApple.show();
	cout<<endl;

	blackApple = greenApple = redApple;
	blackApple.show();
	greenApple.show();
	redApple.show();

	
	return 0;
}

Thak all of you.