Const variable operation error

[Moray Baruh]

I've created a class of complex numbers and defined operations. I've also defined the imaginary unit i as constant in a namespace. When I write

complex z(0,0)
z = z + 2 + i
z = i

Everything works fine. But when I write z = 2 + i , the compiler gives me the error saying Invalid operands to binary expressions ('const complex' and 'int').

Where is my error?

EDIT :
Here is the implementation of the = and + operators in complex.cpp

void complex::operator=(const complex& other){
    realPart = other.realPart;
    imaginaryPart = other.imaginaryPart;
}
void complex::operator=(const double& other){
    realPart = other;
    imaginaryPart = 0;
}
complex complex::operator+(const complex& other){
    complex c = other;
    return complex(realPart + c.realPart, imaginaryPart + c.imaginaryPart);
}
complex complex::operator+(const double& other){
    return operator+(complex(other,0));
}

[firedraco]

You'll have to post the whole error and your complex class for us to help you more.

[Moray Baruh]

Edited the post with the implementation of the operators

[firedraco]

You have no operator defined for operator + (int, complex). Hence, the compiler doesn't know what to do with 2 + i.