Juscallmesteve Juscallmesteve - 27 days ago 6
C++ Question

Overloading the Multiplication Operator

I have looked at many of the other posts dealing with overloading the * operator and I still am unable to see the issue.

#include <iostream>
#include <string>
#include <cmath>

using namespace std;


class Fraction{
private:
int num, den;
public:
void set(int n, int d);
void setNum(int newNum);
void setDen(int newDen);
Fraction add(Fraction other);
Fraction simplify();
Fraction(int new_Num = 0, int new_Den = 0){
num = new_Num;
den = new_Den;
};
void output(Fraction& f);
void cleanerFunction(Fraction& f);
int gcd();
Fraction reduce();
friend ostream& operator <<(ostream& os, Fraction& f);
friend istream& operator >>(istream& in, Fraction& f);
friend Fraction operator + ( const Fraction&, const Fraction& );
friend inline Fraction operator - ( const Fraction&, const Fraction& );
friend Fraction operator * ( const Fraction&, const Fraction& );
friend Fraction operator / ( const Fraction&, const Fraction& );
friend bool operator < ( const Fraction&, const Fraction& );
friend bool operator <= ( const Fraction&, const Fraction& );
friend bool operator > ( const Fraction&, const Fraction& );
friend bool operator >= ( const Fraction&, const Fraction& );
friend bool operator == ( const Fraction&, const Fraction& );

};
int gcd(int x, int y);
Fraction reduce(Fraction f);
void reduce(Fraction& f);

Fraction operator + ( const Fraction& f, const Fraction& r){
int temp_Num, temp_Den;
temp_Num = (f.num * r.den) + (f.den * r.num);
temp_Den = (f.den * r.den);
Fraction temp_Frac(temp_Num, temp_Den);
temp_Frac.cleanerFunction(temp_Frac);
return temp_Frac;

};
Fraction operator - ( const Fraction& f, const Fraction& r){
int temp_Num, temp_Den;
temp_Num = (f.num * r.den) - (f.den * r.num);
temp_Den = (f.den * r.den);
Fraction temp_Frac(temp_Num, temp_Den);
temp_Frac.cleanerFunction(temp_Frac);
return temp_Frac;

};
Fraction operator * ( const Fraction& f, const Fraction& r){
int temp_Num, temp_Den;
temp_Num = (f.num * r.num);
temp_Den = (f.den * r.den);
Fraction temp_Frac(temp_Num, temp_Den);
temp_Frac.cleanerFunction(temp_Frac);
return temp_Frac;
};
Fraction operator / ( const Fraction& f, const Fraction& r){
int temp_Num, temp_Den;
temp_Num = (f.num * r.den);
temp_Den = (f.den * r.num);
Fraction temp_Frac(temp_Num, temp_Den);
return temp_Frac;

};

bool operator < ( const Fraction& f, const Fraction& r){
return (f.num * r.den) < (r.num * f.den);
};
bool operator <= ( const Fraction& f, const Fraction& r){
return (f.num * r.den) <= (r.num * f.den);
};
bool operator > ( const Fraction& f, const Fraction& r){
return (f.num * r.den) > (r.num * f.den);
};
bool operator >= ( const Fraction& f, const Fraction& r){
return (f.num * r.den) >= (r.num * f.den);
};
bool operator == ( const Fraction& f, const Fraction& r ){
return (f.num * r.den) == (r.num * f.den);
};


ostream& operator <<(ostream& os, Fraction& f)
{
f.output(f);
return os;
}

istream& operator >>(istream& in, Fraction& f)
{
char ch;
int temp_Num, temp_Den;
in >> temp_Num >> ch >> temp_Den;
f.set(temp_Num, temp_Den);
f.cleanerFunction(f);
return in;
}

int main()
{
cout <<"HELLO\n";
cout << "Testing declarations " << endl;
cout << "Fraction x, y(2), z(-5,-6), w(1,-3);" << endl;
Fraction x, y(2), z(-5,-6), w(1,-3);
cout << "z = " << z << ", y = " << y << ", z = " << z << ", w = " << w << endl;
cout << "Testing >> overloading: \nEnter a fraction in the format " << "integer _numerator/integer _denominator" << endl;
cin >> x;
cout << "You entered the equivalent of: " << x << endl;
//cout << z << " - (" << w << ") = " << z - w << endl;
cout << "Testing the constructor and normalization routines: " << endl;
y =Fraction(-128, -48);
cout << "y =Fraction(-128, -48) outputs as " << y << endl;
y =Fraction(-128, 48);
cout << "y =Fraction(-128, 48 ) outputs as " << y << endl;
y = Fraction(128,-48);
cout << "y = Fraction(128, -48) outputs as " << y << endl;
Fraction a(1,1);
cout << "Fraction a(1,1); a outputs as: " << a << endl;
Fraction ww = y*a;
cout << y << " * " << a << " = " << ww << endl;
w = Fraction(25,9);
z = Fraction(3,5);
cout << "Testing arithmetic and relational operator overloading" << endl;
//cout << w << " * " << z << " = " << w * z << endl;
//cout << w << " + " << z << " = " << w + z << endl;
//cout << w << " - " << z << " = " << w - z << endl;
//cout << w << " / " << z << " = " << w / z << endl;
cout << w << " < " << z << " = " << (w < z) << endl;
cout << w << " < " << w << " = " << (w < w) << endl;
cout << w << " <= " << z << " = " << (w <= z) << endl;
cout << w << " <= " << w << " = " << (w <= w) << endl;
cout << w << " > " << z << " = " << (w > z) << endl;
cout << w << " > " << w << " = " << (w > w) << endl;
cout << w << " >= " << z << " = " << (w >= z) << endl;
cout << w << " >= " << w << " = " << (w >= w) << endl;
w = Fraction(-21,9);
z = Fraction(3,5);
//cout << w << " * " << z << " = " << w * z << endl;
//cout << w << " + " << z << " = " << w + z << endl;
//cout << w << " - " << z << " = " << w - z << endl;
//cout << w << " / " << z << " = " << w / z << endl;
cout << w << " < " << z << " = " << (w < z) << endl;
cout << w << " < " << w << " = " << (w < w) << endl;
cout << w << " <= " << z << " = " << (w <= z) << endl;
cout << w << " <= " << w << " = " << (w <= w) << endl;
cout << w << " > " << z << " = " << (w > z) << endl;
cout << w << " > " << w << " = " << (w > w) << endl;
cout << w << " >= " << z << " = " << (w >= z) << endl;
cout << w << " >= " << w << " = " << (w >= w) << endl;
return 0;
return 0;
}

Fraction Fraction::add(Fraction other){
Fraction result;
result.num = num*other.den + other.num *den;
result.den = den*other.den;
return result;

}


Fraction Fraction::simplify(){
Fraction f1;
f1.num = 4; f1.den=5;
return f1;

}

int gcd(int x, int y){
if( y<0)
y =-y;

if(x % y == 0)
return y;
else
return gcd(y, x%y);
}

int Fraction::gcd(){
Fraction temp;
if( den<0)
den =-den;

if(num % den == 0)
return den;
else{
temp.num =den;
temp.den= num%den;
return temp.gcd();
}
}

void Fraction::set(int n, int d){
num = n;
den = d;

}

void Fraction::setNum(int newNum){
num = newNum;
}
void Fraction::setDen(int newDen){
den = newDen;
}
Fraction Fraction::reduce(){
Fraction temp;
temp.set(num,den);
int m = temp.gcd();
num /= m;
den /= m;
}
Fraction reduce(Fraction f){
int m = f.gcd();

}
void reduce(Fraction& f){

}

void Fraction::output(Fraction& f){

f.cleanerFunction(f);
cout << num << "/"<< den;
}

void Fraction::cleanerFunction(Fraction& f){
int temp_Num = num;
int temp_Den = den;

if ((temp_Num != 0) && (temp_Den == 0))
temp_Den = 1;
if ((temp_Num > 0) && (temp_Den < 0 )){
temp_Den = abs(temp_Den);
temp_Num = -temp_Num;
};
if (( temp_Num < 0) && (temp_Den < 0)){
temp_Den = abs(temp_Den);
temp_Num = abs(temp_Num);
};

num = temp_Num;
den = temp_Den;
}


There is the relevant code, if you need more I can post. The code *cout << w * z << endl; * and everything in Main() cannot be modified, everything else can.

Error I get is
error: cannot bind 'std::ostream {aka std::basic_ostream}' lvalue to 'std::basic_ostream&&'

The commented out lines in Main() are the lines where I get error messages. So I get problems with the (+,-,*,/) operators. I wanted to just look at the * so I could then go back and apply the same fix to the rest of those.

Answer

You get error message at cout << w * z << endl; because there is no overload of operator<< which takes class Fraction as an argument. Try defining this overload:

std::ostream& operator<<(std::ostream& os, const Fraction& f)
{
    return os << f.den << "/" << f.num;
}

And add the following line to the definition of class Fraction in order to make den and num available to this function:

friend std::ostream& operator<<(std::ostream& os, const Fraction& f);