Giving one class Access to another C++

Question

I am trying to access a member of one class in another class. I am fairly new to C++ so forgive me if this is an easy fix but I cannot find the answer, so I came here.

In this instance I would like to call "init();" from class CGuessNumber and member CheckNumber.

Here is my code.

#include <iostream>
#include <ctime>
#include <cstdlib>

class CGuessNumber
{
public:
    int GenerateNumber()
    {
        return rand() % 100 + 1;
    }

    void checkNumber(int guess, int answer, int &attempts)
{

    if (guess < answer)
    {
        std::cout << "TOO LOW, TRY AGAIN"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        attempts--;
    }else if(guess > answer)
    {
        std::cout << "TOO HIGH, TRY AGAIN"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        attempts--;
    }else if(guess ==  answer)
    {
        std::cout << "YOU WON!"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
    }

    if (attempts <= 0)
    {
        std::cout << "YOU LOST!"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        CGAME::init(answer, attempts);
    }

}
}Number;

class CGAME
{
public:
        void init(int &answer, int &attempts)
    {
        answer = Number.GenerateNumber();
        attempts = 5;
    };

    int newGame()
    {
        srand (time(NULL));
        int intAnswer, playerGuess, trys;

        init(intAnswer, trys);

        while(intAnswer != playerGuess and trys > 0)
        {
            std::cin >> playerGuess;

            Number.checkNumber(playerGuess, intAnswer, trys);
        }
    };
}ONewGame;

int main()
{
    CGAME ONewGame
    ONewGame.newGame();

    return 0;
}

Answer 1

Let me just address the syntax errors.

In the checkNumber() function:

...
CGAME::init(answer, attempts);
...

There are 2 problems with this:

1. CGAME is not declared yet, so the compiler doesn't know it exists, or what it is. To avoid this, usually all the classes are declared at the top (or in a header file) and all there functions are defined later.

2. You can't call a member function of a class without an object, unless it's a static function. This function can be static as it doesn't use member variables (there are design issues, but lets ignore them for now).

Also in main() you missed a ';', but I think you already know that :-)

So, applying these changes:

#include <iostream>
#include <ctime>
#include <cstdlib>

// only declaring the classes here
class CGAME
{
public:
    static void init(int &answer, int &attempts);
    int newGame();
}ONewGame;

class CGuessNumber
{
public:
    int GenerateNumber();
    void checkNumber(int guess, int answer, int &attempts);
}Number;

// defining all the class member functions now
int CGAME::newGame()
{
    srand (time(NULL));
    int intAnswer, playerGuess, trys;

    init(intAnswer, trys);

    while(intAnswer != playerGuess and trys > 0)
    {
        std::cin >> playerGuess;

        Number.checkNumber(playerGuess, intAnswer, trys);
    }
}

int CGuessNumber::GenerateNumber()
{
    return rand() % 100 + 1;
}

void CGuessNumber::checkNumber(int guess, int answer, int &attempts)
{
    if (guess < answer)
    {
        std::cout << "TOO LOW, TRY AGAIN"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        attempts--;
    }else if(guess > answer)
    {
        std::cout << "TOO HIGH, TRY AGAIN"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        attempts--;
    }else if(guess ==  answer)
    {
        std::cout << "YOU WON!"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
    }

    if (attempts <= 0)
    {
        std::cout << "YOU LOST!"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        CGAME::init(answer, attempts);
    }
}

void CGAME::init(int &answer, int &attempts)
{
    answer = Number.GenerateNumber();
    attempts = 5;
}

int main()
{
    CGAME ONewGame;
    ONewGame.newGame();

    return 0;
}

Answer 2

I think, this is what you're looking for

Basically you can pass a pointer which points to one object into a constructor of the other. In this case we just pass a pointer to CGuessNumber into the CGAME constructor, we also store this pointer in a private field so we can use it. Then you can use this pointer to call methods.

working example (pointer->method syntax)

working example (reference.method syntax)

#include <iostream>
#include <ctime>
#include <cstdlib>

class CGuessNumber
{
public:

    int GenerateNumber()
    {
        return rand() % 100 + 1;
    }

void checkNumber(int guess, int answer, int &attempts)
{

    if (guess < answer)
    {
        std::cout << "TOO LOW, TRY AGAIN"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        attempts--;
    }else if(guess > answer)
    {
        std::cout << "TOO HIGH, TRY AGAIN"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
        attempts--;
    }else if(guess ==  answer)
    {
        std::cout << "YOU WON!"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
    }

    if (attempts <= 0)
    {
        std::cout << "YOU LOST!"  << "\n" << "TRYS LEFT: " << attempts  << "\n";
    }
}
};

class CGAME
{
public:

    CGAME(CGuessNumber* pNumber)
    {
        m_number = pNumber;
    }
    void init(int &answer, int &attempts)
    {
        answer = m_number->GenerateNumber();
        attempts = 5;
    };

    void newGame()
    {
        srand (time(NULL));
        int intAnswer, playerGuess, trys;

        init(intAnswer, trys);

        while(intAnswer != playerGuess and trys > 0)
        {
            std::cin >> playerGuess;

            m_number->checkNumber(playerGuess, intAnswer, trys);
        }
    };

    private:
        CGuessNumber* m_number;
};

int main()
{
    CGuessNumber* pGnum = new CGuessNumber();
    CGAME* ONewGame = new CGAME(pGnum);
    ONewGame->newGame();
    return 0;
}