How can I implement a friendly function to subtract two numbers m1 and m2?

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How can I implement a friendly function to subtract two numbers m1 and m2?

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#1 by (2 votes)

1

The function that adds them is given by: In the file that contains the int main ():

 add(m1,m2, sum); 
 cout << "The sum is:"; 
 sum.display_money();

In the .h file:

 friend void add(AltMoney m1, AltMoney m2, AltMoney& sum);

In the .cpp file

void add(AltMoney m1, AltMoney m2, AltMoney& sum) 
{
 int extra = 0; 
 sum.cents = m1.cents + m2.cents; 
 if(sum.cents >=100){ 
     sum.cents = sum.cents - 100; 
     extra = 1; 
 }

 sum.dollars = m1.dollars + m2.dollars + extra; 
}

From that implementation I want to subtract one from the other ...

The sum I am calling by reference, but I can not find the logic to subtract.

Thanks for your time and help.

c++

asked by Gabriel Valedon 12.02.2017 в 18:05

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1 answer

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score 2 · Answer 1

Friendly functions allow access to private data objects as if this function had the permissions of member functions; without declaring the function as a friend, the usual restrictions apply, for example:

class C
{
    int i;
};

void Suma_1(C &c)
{
    ++c.i; // Error, 'C::i' es privado!
}

int main()
{
    C c;
    Suma_1(c);
    return 0;
}

For a function to be considered a friend, you must declare yourself inside the object that you want to grant access to; in this way the friendly function will obtain the same access levels as the members of that object:

class C
{
    // Declaramos la funcion 'Suma_1' como amiga de la clase 'C'.
    friend void Suma_1(C &);
    int i;
};

void Suma_1(C &c) // Definimos la funcio 'Suma_1'.
{
    ++c.i; // Correcto, 'C::i' es privado, pero 'Suma_1' es amiga.
}