mdistance and edistance addition via friend

A friend function is not a member of a class but can access its private members if the class declares it with the keyword friend. Here one function add() is declared as a friend of both classes, so it can read the private data of both mdistance (metre, centimetre) and edistance (feet, inches).

Assumptions: 1 m = 100 cm, 1 ft = 12 in, 1 in = 2.54 cm. The sum is displayed in metres and centimetres.

#include <iostream>
using namespace std;

class edistance;                 // forward declaration

class mdistance {
    int meter;
    float cm;
public:
    void getdata() {
        cout << "Enter meter and centimeter: ";
        cin >> meter >> cm;
    }
    friend void add(mdistance, edistance);
};

class edistance {
    int feet;
    float inch;
public:
    void getdata() {
        cout << "Enter feet and inches: ";
        cin >> feet >> inch;
    }
    friend void add(mdistance, edistance);
};

// friend of both classes
void add(mdistance m, edistance e) {
    // convert everything to centimetres
    float total_cm = m.meter * 100 + m.cm
                   + (e.feet * 12 + e.inch) * 2.54;
    int mt = (int)(total_cm / 100);
    float c = total_cm - mt * 100;
    cout << "Sum = " << mt << " m " << c << " cm" << endl;
}

int main() {
    mdistance m;
    edistance e;
    m.getdata();
    e.getdata();
    add(m, e);
    return 0;
}

Sample run:

Enter meter and centimeter: 2 50
Enter feet and inches: 3 6
Sum = 3 m 56.68 cm

Check: 3 ft 6 in = 42 in = 106.68 cm; 2 m 50 cm = 250 cm; total = 356.68 cm = 3 m 56.68 cm.