how to compare two objects in c++ code example

Example: compare two functions in a class c++

class Date
{
public:
Date();                                  // Constructor without parameters
Date(int m, int d, int y); // Constructor with parameters.

// accessors
int GetMonth();               // returns the size of the diamond
int GetDay();
int GetYear();

// mutators
bool Set(int m, int d, int y);
bool SetFormat(char f);

// standard input and output routines
void Input();             
void Show();              
void Increment(int numDays = 1);                 
int Compare(const Date& d);     

private:
int month,                    // month variables
    day,                 // day variable
    year;               // year variable
char format;
};