Initialize variables in a class method?

Question

I have a silly question:

I have a class and in one of its methods I have to do some calculations and I need to declare some variables that are useful to do this. For example:

class Percettrone {
public:
    Percettrone(double NL);
    void fit(double X, double y);
}
.
.
.
void Percettrone::fit(double X, double y)
{
        double delta[50][50];
        double conteggio=0;
        //calculations
}

Is it correct? Or is it better to declare when I create the class? Moreover I have to call this method lots of time during my programme

Answer 1

If those variables are affecting the object instance and identifying its state, then you must declare them in the class as attributes. On the other hand, if they're just helper variables in the function, and you don't need to use them anywhere else, then make them local inside the function as you did in the example.