Unary (++) Operator Overloading using Friend Function

This is the solution that increases an integer value by 1 by overloaded operator using Friend Function (T.U. 2072)

#include <iostream>

using namespace std;

class Increment
{
    int a;
public:
    Increment()
    {
        a=0;
    }
    Increment(int x)
    {
        a=x;
    }
    friend operator++(Increment &I,int); //Use & while using Friend Function
    friend operator++(Increment &I);
    void print();
};

operator++(Increment &I,int)
{
    I.a++;
}
operator++(Increment &I)
{
    ++I.a;
}

void Increment::print()
{
    cout << endl << "a=" << a << endl ;
}

int main()
{
    Increment I1;
    I1.print();
    I1++;
    I1.print();
    Increment I2(100);
    I2.print();
    ++I2;
    I2.print();
    return 0;
}