Issue with a friend function in a class in C++? - c++

Question

I have a class with 3 fields a,b and c. I want to calculate the volume of a box with sides a,b or c. I want to do this with a friend function. However, when I compile the program the Compiler gives an error No global operator found which takes type Box. I would like to ask why is that?
#include "pch.h"
#include <iostream>
using namespace std;
class Box {
double a, b, c;
public:
Box(double sa, double sb, double sc) {
a = sa;
b = sb;
c = sc;
}
friend double calcVolume(Box bx) {
return bx.a*bx.b*bx.c;
};
};
int main() {
Box a(5.67, 6.43, 7.00),b(90,32.76,44.18);
cout << calcVolume(a)<<endl;
return 0;
}

Answer 1

There is a mistake in you code return bx.a*bx.b*bx*c;, which should be return bx.a*bx.b*bx.c; (the last dot)
#include <iostream>
using namespace std;
class Box {
double a, b, c;
public:
Box(double sa, double sb, double sc) {
a = sa;
b = sb;
c = sc;
}
friend double calcVolume(Box &bx) {
return bx.a * bx.b * bx.c;
};
};
int main() {
Box a(5.67, 6.43, 7.00),b(90,32.76,44.18);
cout << calcVolume(a)<<endl;
return 0;
}

Answer 2

A couple of things : use const when you are not modifying the argument, second do not do using namespace std. Now, this works for me
#include <iostream>
class Box
{
double a;
double b;
double c;
public:
Box(double ain, double bin, double cin) {a = ain; b = bin; c = cin;}
friend double calcVol(const Box& rOther)
{
return rOther.a*rOther.b*rOther.c;
}
};
int main()
{
Box a(14.8, 10.8, 11.01), b(8,5.0,6.2);
std::cout<<"vol a :: "<<calcVol(a)<<std::endl;
std::cout<<"vol b :: "<<calcVol(b)<<std::endl;
return 0;
}