friend

[DarkParadox]

Why does this program doesn't work??

#include<iostream>
#define pi 3.141592654
using namespace std;

class Triangle
{
    int base, height;
   public:
    friend Triangle set_value(int,int);
    int area()
    {
        return 5e-1*base*height;
    }
};

Triangle set_value(int a, int b)
{
    Triangle lol;
    lol.base  = a;
    lol.height = b;
    return lol;
}

class Circle
{
    float radius;
   public:
    friend Circle set_value(int a)
    {
        Circle n;
        n.radius = a;

    }
    float area();
};

float Circle :: area()
{
    return pi*radius*radius;
}

int main()
{
    Triangle tri;
    Circle cir;
    int n,m,r;
    cout << "Triangle size = ";
    cin >> n >> m;
    cout << "Circle size = ";
    cin >> r;
    system("cls");
    tri = set_value(n,m);
    cir = set_value(r);
    cout << "Triangle area = " << tri.area();
    cout << "\nCircle Area = " << cir.area();
}

|53|error: too few arguments to function 'Triangle set_value(int, int)'|

According to the compiler, that is the error, but cir is a Circle class and I have set the set_value in Circle class to have only have 1 variable as parameterfriend Circle set_value(int a), so why is it error?

[Repeater]

cir = set_value(r);

This is an attempt to call the function
Triangle set_value(int a, int b)

As you can see, the function takes another int.

I have set the set_value in Circle class to have only have 1 variable

That's true, but you're not calling the class function Circle::set_value(int), are you? You're calling the function Triangle set_value(int a, int b)

If you want to call a class function, you have to call it on an object of that class.

 Circle cir; // Create an object of class Circle
 cir.set_value(5); // Call the function Circle::set_value(int) on the object of class Circle
 set_value(6, 7); // Call the non-class function Triangle set_value(int a, int b) 

[ne555]

@Repeater: there is no member function Circle::set_value(int)
notice that it is declared as friend and defined inline, it's a free (global) function, not a member function

as to why the compiler can't see it, the lookup method changes
https://stackoverflow.com/a/382077 (the example uses an operator, but the same may be said about a function)

It makes the operator not visible to normal lookup. The only way you can call it is using argument dependent look-up. This will keep the namespace free of lots of operator declarations visible normally.

as to how to solve it, well, remove such a crappy friend function
you may use a constructor, that's what they are for.

[Repeater]

So there isn't. That's me told for reading it too fast.