Error while overloading operator +,-,*,/ in c++ [duplicate] - c++

Question

This question already has answers here:
What are the basic rules and idioms for operator overloading?
(8 answers)
Closed 6 years ago.
I am getting error while trying to compile the following code. I am beginner. Please help me figuring it out. I am trying to overload the operators _,+,/,*. It shows error while compiling. Should I use "friend" to solve this?
#include<stdio.h>
class complex{
private:
double real; //real part of complex
double imag; // imaginary part of complex
public:
complex(double r=0., double i=0.):real(r),imag(i)
{
} // constructor with initialization
complex(const complex&c):real(c.real),imag(c.imag)
{
} // copy constructor with initialization
~complex()
{
} // destructor
double re() const
{
return real;
} // read real part
double im() const
{
return imag;
} // read imaginary part
const complex& operator=(const complex&c)
{
real=c.real;
imag=c.imag;
return *this;
} //assignment operator
const complex& operator+=(const complex&c)
{
real += c.real;
imag += c.imag;
return *this;
} // addition of current complex
const complex& operator-=(const complex&c)
{
real -= c.real;
imag -= c.imag;
return *this;
} // subtract from current complex
const complex& operator*=(const complex&c)
{
double keepreal = real;
real = real*c.real-imag*c.imag;
imag = keepreal*c.imag+imag*c.real;
return *this;
} // multiply current complex with a complex
const complex& operator/=(double d)
{
real /= d;
imag /= d;
return *this;
} // divide current complex with real
void print(const complex&c)
{
printf("(%f,%f)\n",c.re(),c.im() );
} // printing complex number
friend complex operator !(const complex& c)
{
return complex(c.re(),-c.im());
}
friend double abs2(const complex& c)
{
return c.re()*c.re()+c.im()*c.im();
} // absolute value of complex
const complex& operator/=(const complex&c)
{
return *this *= (!c)/=abs2(c);
} // divide the current complex by a complex
const complex operator-(const complex& c)
{
return complex(-c.re(),-c.im());
} // negative of complex number
const complex operator-(const complex& c,const complex& d)
{
return complex(c.re()-d.re(),c.im()-d.im());
} // difference between complex numbers
const complex operator+(const complex& c,const complex& d)
{
return complex(c.re()+d.re(),c.im()+d.im());
} // addition of complex numbers
const complex operator*(const complex& c,const complex& d)
{
return complex(c)*=d;
} // multiplication of complex numbers
const complex operator/(const complex& c,const complex& d)
{
return complex(c)/=d;
} // division of complex numbers
};
int main(){
complex c(1.,0.),d(3.,4.);
print(c-d);
print(c/d);
return 0;
}
the output I am getting is:
complex_nums.cpp:76:59: error: ‘const complex complex::operator-(const complex&, const complex&)’ must take either zero or one argument
const complex operator-(const complex& c,const complex& d)
^
complex_nums.cpp:80:59: error: ‘const complex complex::operator+(const complex&, const complex&)’ must take either zero or one argument
const complex operator+(const complex& c,const complex& d)
^
complex_nums.cpp:84:59: error: ‘const complex complex::operator*(const complex&, const complex&)’ must take either zero or one argument
const complex operator*(const complex& c,const complex& d)
^
complex_nums.cpp:88:59: error: ‘const complex complex::operator/(const complex&, const complex&)’ must take exactly one argument
const complex operator/(const complex& c,const complex& d)
^
complex_nums.cpp: In function ‘int main()’:
complex_nums.cpp:96:11: error: ‘print’ was not declared in this scope
print(c-d);
^
complex_nums.cpp:97:9: error: no match for ‘operator/’ (operand types are ‘complex’ and ‘complex’)
print(c/d);

Answer 1

All your operators (+,-,*,/) need exactly one or no arguments, unless they are friend functions. Mark all the operator functions as friend, and the code should work. Otherwise, eliminate 1 parameter from each of the operators, and instead of that use the current instance (this). Example for + operator with parameter removed:
const complex operator+(const complex& c)
{
return complex(c.re()+re(),c.im()+im());
}
Reference of friend arithmetic operators: http://www.learncpp.com/cpp-tutorial/92-overloading-the-arithmetic-operators-using-friend-functions/
Next Error
What are you doing with your print() function? It should be in global scope, because it takes a complex as parameter. Move print() out of the class into global scope, like this. If you still want to keep a print() for the object itself, do so, but the one for your class should look like below:
class complex
{
void print(const complex&c)
{
printf("(%f,%f)\n",re(),im() );
} // printing complex number
};
void print(const complex&c)
{
printf("(%f,%f)\n",c.re(),c.im() );
} // printing complex number

Answer 2

Binary operators are either free functions with 2 arguments (preferred) or member functions with one argument (not so good).
You have defined member functions with 2 arguments.
Turning them into free functions by adding friend is one way.
Another is to make them free functions, defined outside the class but written in terms of member functions (as you have done anyway):
struct complex
{
/* ... */
};
// class definition ends
//free function
inline complex operator/(const complex& c,const complex& d)
{
return complex(c)/=d;
} // division of complex numbers
Note, this function can be improved:
inline complex operator/(complex c,const complex& d)
{
c /= d;
return c;
}
Also, unary operators should return complex&, not const complex&. The thing you're returning is mutable, because you just mutated it.

Answer 3

For the errors with the operators must take either zero or one argument, this is because you are implementing the non-member function as a member funciton. These should be free functions to work properly, or should only take one argument and use this as the other.
See this question for clarification:
Operator overloading : member function vs. non-member function?
For the error with print, I guess you are trying to call the print member function. To do that you need to do e.g. the following:
complex(c-d).print();