Question

Consider the following code:

#include<iostream>
using namespace std;
class sample
{
    int a;
    int b;
public:
    void setValue()
    {
        a=25;
        b=40;
    }
    friend float mean(sample s)
    {
        return float(s.a+s.b)/2.0;
    }
}
int main()
{
    sample x;

    x.setValue();
    cout<< "mean value:"<< mean(x)<<endl;

    cin.ignore();
    getchar();
    return (0);
}

I expected this to output when attempting to compile and run it:

mean value: 32.5

However, I get these compiler errors isntead:

1>  frndF.cpp
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(18): error C2628: 'sample' followed by 'int' is illegal (did you forget a ';'?)
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(19): error C3874: return type of 'main' should be 'int' instead of 'sample'
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(27): error C2664: 'sample::sample(const sample &)' : cannot convert parameter 1 from 'int' to 'const sample &'
1>          Reason: cannot convert from 'int' to 'const sample'
1>          No constructor could take the source type, or constructor overload resolution was ambiguous
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(15): warning C4244: 'return' : conversion from 'double' to 'float', possible loss of data

What did I do wrong?

Answer 1

You forgot the semicolon after the closing bracket of the class definition:

class sample
{
   //code omitted for brevity

}; <------------------- you forgot this

---

Although, this has nothing to do with the error or expected output, you should pass the argument to mean() by const reference as:

friend float mean(sample const & s)
{                      //^^^^^^^ const reference
    return float(s.a+s.b)/2.0;
}

This avoids unnecessary copy of the argument.