C++ operator overloading method

Question

I'm working through some home work and having problems with how to form my method signature for overloading a member of a class.

My header file

class MyInt
{
    int internalInt;
public:
    MyInt::MyInt(int i);
    const MyInt operator+(const MyInt& mi);
    const MyInt& operator++();
};

My code file

MyInt::MyInt(int i)
{
    internalInt = i;
}

const MyInt MyInt::operator+(const MyInt& mi)
{
    cout << "Inside the operator+\n";
    mi.print(cout);
    return MyInt(internalInt + mi.internalInt);
}

const MyInt& MyInt::operator++()
{
    cout << "Inside the operator++\n";
    internalInt++;
    return this; //Line 42
}

When I try to compile the code I'm getting an error that says

ex4.cpp:42: error: invalid initialization of reference of type ‘const MyInt&’ 
from expression of type ‘MyInt* const’

I'm having problems understanding how to get this working and have tried a few method signatures. In my text book they are in lining all the overloads but I was hoping to figure out what I'm doing wrong instead of just going with the flow to get my code to compile.

Thanks!

Answer 1

First of all, in operator++(), write return *this; instead of return this;. Also remove the const!

-

 const MyInt operator+(const MyInt& mi);

Second, Make it const-function, as

 const MyInt MyInt::operator+(const MyInt& mi) const // <--- note this!

This is const-function. Without it, you would not be able to add const objects of MyInt.

After you write const on the right most side, you can write this:

const MyInt m1(10);
MyInt m2(20);
MyInt m3 = m1 + m2 ; //m1 is const, so it can call ONLY const-function

Answer 2

try:

const MyInt& MyInt::operator++()
{
    cout << "Inside the operator++\n";
    internalInt++;
    return *this;
}

You are returning the this pointer, not the reference, you need to dereference it.