Multiple Classes

[Nathaniel10]

I have a difficulty I need help to overcome. I am developing a program that uses more than 1 class. Variables defined in one class are used in other classes. For example:

class X1 {
private:
   int a;
   int b;
public;
   X1() {
      a = 10;
      b = 20;
   }
};

class X2 {
private:
   int c;
   int d;
public;
   X2() {
      c = 5 + 2*a;
      d = 10 - 4*b;
   }
};

int main() {
   X2 Test;
   int e = 40 + 10*d;
   cout << e << endl;

   keep_window_open();
   return 0;
}

I get a compile error that variable a and b in class X2 are not declared and initialized. I tried making X2 a sub-class of X1, hoping that X2 would inherit the variables a and b, but IO got even more compile errors.

My question: Is there a way to link the classes so that the variables of a prior class are known and usable in the subsequent classes? Or will I have to make one HUGE class?

Thanks in advance.

[Ancient Dragon]

you have to make x1 the base class of x2. Study up on ingerentence. In your example X2 will be unable to access the private variables of X1 -- you will have to make those variables either protected or public.

class X2 : public X1
{
   // blabla
};

[mrnutty]

Before resorting to inheritance, can you state your actual problem with some actual context? Maybe you have been going about this problem wrong?

[Nathaniel10]

Stroustrup has an exercise in which the reader makes the "Hunt the Wumpus" game. My first step was to create the starting room. This is that code:

#include "../../std_lib_facilities.h"

class Initialize {
private:
	double rand_wumpus;
	double rand_pit;
	double rand_bat;

public:
	Initialize() {
	double srand((unsigned)time(0));
        rand_wumpus = 100.0 * rand()/RAND_MAX;
        rand_pit = 100.0 * rand()/RAND_MAX;
        rand_bat = 100.0 * rand()/RAND_MAX;
	}
};


class Current_room {
private:
	int room_num;
	bool wumpus_in_room;
	bool pit_in_room;
	bool bat_in_room;

public:
	Current_room() {
        if (rand_wumpus > 10.5 && rand_wumpus < 12.2) {
		wumpus_in_room = true;
		cout << "The wumpus is in the room.  You are eaten!" << endl;
	} else {
		wumpus_in_room = false;
	}

	if (rand_pit > 30.1 && rand_pit < 41.8) {
		pit_in_room = true;
		cout << "You have fallen into a pit and died!" << endl;
	} else {
		pit_in_room = false;
	}

    if (rand_bat > 62.4 && rand_bat < 75.0) {
		bat_in_room = true;
		cout << "A bat has taken you to another room!" << endl;
	} else {
		bat_in_room = false;
	}
	if (wumpus_in_room == false && pit_in_room == false && bat_in_room == false) {
		cout << "You are safe!" << endl;
	}
	}
};


int main()
{
Current_room Test;

keep_window_open();
return 0;
}

The Current_room class is not accessing the rand_wumpus, rand_pit, and rand_bat variables form the Initialize class. The suggestions are to make Initialize public, use get() functions for those variables, or make Current_room a sub-class of Initialize. I don't which is best.

[mrnutty]

There is not point for Initialize class to have the member private. You would be better of making them priviate. Also Initialize is a bad name. Call it something more meaningful and clear.

[Nathaniel10]

This thread has been continued in "Wumpus Hunt".