Rational(long n,long d):N(n),D(d)

[msdagiya]

A constructor is declared inside a class. but I didn't understand what N(n) and D(d) are. note that N and D are two private members of class Rational. does any one know?

Rational(long n,long d):N(n),D(d){

}

[Chervil]

It's initialisation. The effect is similar to this:

Rational(long n,long d) {
    N = n;
    D = d;
}