Just started C++: Undefined Symbol error on Compile

Question

Here's the situation:

I just started my first C++ class. I know nothing about C++ and despite this being the an intro to C++ class, the teacher has taught pretty much NO syntax for the language, just logic that we already know.

Now he gave us a program description and said, "write it, lol." I understand the logic fine, but as I said before, I know nothing about C++. Thus I wrote it first in java (which I do know), and then once I got it working in java, I tried to code it over to C++.

However now I am getting the following error when I compile

uxb3% g++ -o Race race.cc
Undefined                       first referenced
 symbol                             in file
main                                /usr/local/gcc-4.1.1/bin/../lib/gcc/sparc-sun-solaris2.10/4.1.1/crt1.o
ld: fatal: Symbol referencing errors. No output written to Race
collect2: ld returned 1 exit status

Can someone please help me with this?

Here is my code in a .txt file: http://rapidshare.com/files/195742284/race.txt.html

and here it is in a copy paste:

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

using namespace std;
class Race
{

        void main()
        {
                executeRace();
        }

        int randomMove()
        {
                srand(time(NULL));
                int randomInt = rand() % 100 + 1;
                return randomInt;
        }

        void executeRace()
        {
                int rabbitPosition = 1;
                int turtlePosition = 1;

                cout << "BANG!!!" << endl << "AND THEY'RE OFF!!!";

                while (rabbitPosition <=70 && turtlePosition <=70)
                {
                        printPositions(rabbitPosition, turtlePosition);

                        turtlePosition = turtleMoveSquares(turtlePosition);
                        rabbitPosition = rabbitMoveSquares(rabbitPosition);
                }

                printWinner(rabbitPosition, turtlePosition);

                tie(rabbitPosition, turtlePosition);
        }

        int turtleMoveSquares(int tPosition)
        {

                int turtleMove = randomMove();

                if(turtleMove >=1 && turtleMove <= 40)
                        tPosition = tPosition + 4;

                if(turtleMove >= 41 && turtleMove <= 50 )
                        tPosition = tPosition - 2;

                if(turtleMove >=51 && turtleMove <=100)
                        tPosition = tPosition + 2;

                if(tPosition < 1)
                        tPosition = 1;

                return tPosition;
        }


        int rabbitMoveSquares(int rabbitPosition)
        {

                int rabbitMove = randomMove();

                if(rabbitMove >=1 && rabbitMove <= 25)
                        rabbitPosition = rabbitPosition;

                if(rabbitMove >=26 && rabbitMove <= 55)
                        rabbitPosition = rabbitPosition + 10;

                if(rabbitMove >=56 && rabbitMove <=60)
                        rabbitPosition = rabbitPosition - 15;

                if(rabbitMove >=61 && rabbitMove <= 90)
                        rabbitPosition = rabbitPosition + 5;

                if(rabbitMove >=90 && rabbitMove <=100)
                        rabbitPosition = rabbitPosition - 3;

                if(rabbitPosition < 1)
                        rabbitPosition = 1;

                return rabbitPosition;
        }

        void printPositions(int rabbitPositions, int turtlePositions)
        {
                int turtleCount;
                int rabbitCount;
                int endCount;

                if(rabbitPositions == turtlePositions && rabbitPositions != 1)
                {
                        turtleCount = 1;

                        while(turtleCount < turtlePositions)
                        {
                                cout << "-";
                                turtleCount = turtleCount+1;
                        }
                        cout << "OUCH!";
                }

                else
                {
                        turtleCount = 1;
                        rabbitCount = 1;
                        endCount=1;

                        if(turtlePositions < rabbitPositions)
                        {
                                while(turtleCount < turtlePositions)
                                {
                                        cout <<  "-";
                                                turtleCount = turtleCount+1;
                                }

                                cout << "T";

                                while(rabbitCount < (rabbitPositions - turtlePositions))
                                {
                                        cout <<  "-";
                                        rabbitCount = rabbitCount+1;
                                }
                                cout << "H";

                        }

                        if(rabbitPositions < turtlePositions)
                        {
                                while(rabbitCount < rabbitPositions)
                                {
                                        cout << "-";
                                                rabbitCount = rabbitCount+1;
                                }
                                cout << "H";

                                while(turtleCount < (turtlePositions - rabbitPositions))
                                {
                                        cout << "-";
                                        turtleCount = turtleCount+1;
                                }
                                cout << "T";

                                cout << "\n";
                        }
                }
        }

        void printWinner(int rabbitPosition, int turtlePosition)
        {
                if(turtlePosition >= 70 && rabbitPosition < 70)
                {
                        cout << "TORTOISE WINS!!! YAY!!!\n";
                }
                else if(rabbitPosition >=70 && turtlePosition < 70)
                {
                        cout << "Hare wins. Yuch.\n";
                }
                else if(rabbitPosition >=70 && turtlePosition >=70)
                {
                        cout << "It's a tie\n";
                }
        }

        void tie(int turtlePosition, int rabbitPosition)
        {
                if(rabbitPosition >=70 && turtlePosition >=70)
                        executeRace();
        }
};

Answer 1

You have no main function.

C++'s biggest difference from Java is that its main() function has this signature (parameters optional):

int main(int argc, char** argv);

And it is in the global namespace. This is the function invoked at program start, and probably why you're missing a symbol.

Try adding this to your program:

int main() {
    Race r;
    r.main();
    return 0;
}

Alternatively, you can do away with the class entirely since you're not actually doing anything with it.

Answer 2

Perhaps this is what you meant

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

using namespace std;



class Race
{

public:
    void ExecuteRace()
    {
        int rabbitPosition = 1;
        int turtlePosition = 1;

        cout << "BANG!!!" << endl << "AND THEY'RE OFF!!!";

        while (rabbitPosition <=70 && turtlePosition <=70)
        {
            printPositions(rabbitPosition, turtlePosition);

            turtlePosition = turtleMoveSquares(turtlePosition);
            rabbitPosition = rabbitMoveSquares(rabbitPosition);
        }

        printWinner(rabbitPosition, turtlePosition);

        tie(rabbitPosition, turtlePosition);
    }

private:
    int randomMove()
    {
        srand(time(NULL));
        int randomInt = rand() % 100 + 1;
        return randomInt;
    }


    int turtleMoveSquares(int tPosition)
    {

        int turtleMove = randomMove();

        if(turtleMove >=1 && turtleMove <= 40)
            tPosition = tPosition + 4;

        if(turtleMove >= 41 && turtleMove <= 50 )
            tPosition = tPosition - 2;

        if(turtleMove >=51 && turtleMove <=100)
            tPosition = tPosition + 2;

        if(tPosition < 1)
            tPosition = 1;

        return tPosition;
    }


    int rabbitMoveSquares(int rabbitPosition)
    {

        int rabbitMove = randomMove();

        if(rabbitMove >=1 && rabbitMove <= 25)
            rabbitPosition = rabbitPosition;

        if(rabbitMove >=26 && rabbitMove <= 55)
            rabbitPosition = rabbitPosition + 10;

        if(rabbitMove >=56 && rabbitMove <=60)
            rabbitPosition = rabbitPosition - 15;

        if(rabbitMove >=61 && rabbitMove <= 90)
            rabbitPosition = rabbitPosition + 5;

        if(rabbitMove >=90 && rabbitMove <=100)
            rabbitPosition = rabbitPosition - 3;

        if(rabbitPosition < 1)
            rabbitPosition = 1;

        return rabbitPosition;
    }

    void printPositions(int rabbitPositions, int turtlePositions)
    {
        int turtleCount;
        int rabbitCount;
        int endCount;

        if(rabbitPositions == turtlePositions && rabbitPositions != 1)
        {
            turtleCount = 1;

            while(turtleCount < turtlePositions)
            {
                cout << "-";
                turtleCount = turtleCount+1;
            }
            cout << "OUCH!";
        }

        else
        {
            turtleCount = 1;
            rabbitCount = 1;
            endCount=1;

            if(turtlePositions < rabbitPositions)
            {
                while(turtleCount < turtlePositions)
                {
                    cout <<  "-";
                    turtleCount = turtleCount+1;
                }

                cout << "T";

                while(rabbitCount < (rabbitPositions - turtlePositions))
                {
                    cout <<  "-";
                    rabbitCount = rabbitCount+1;
                }
                cout << "H";

            }

            if(rabbitPositions < turtlePositions)
            {
                while(rabbitCount < rabbitPositions)
                {
                    cout << "-";
                    rabbitCount = rabbitCount+1;
                }
                cout << "H";

                while(turtleCount < (turtlePositions - rabbitPositions))
                {
                    cout << "-";
                    turtleCount = turtleCount+1;
                }
                cout << "T";

                cout << "\n";
            }
        }
    }

    void printWinner(int rabbitPosition, int turtlePosition)
    {
        if(turtlePosition >= 70 && rabbitPosition < 70)
        {
            cout << "TORTOISE WINS!!! YAY!!!\n";
        }
        else if(rabbitPosition >=70 && turtlePosition < 70)
        {
            cout << "Hare wins. Yuch.\n";
        }
        else if(rabbitPosition >=70 && turtlePosition >=70)
        {
            cout << "It's a tie\n";
        }
    }

    void tie(int turtlePosition, int rabbitPosition)
    {
        if(rabbitPosition >=70 && turtlePosition >=70)
            ExecuteRace();
    }
};


void main()
{
    Race race;
    race.ExecuteRace();
}

Answer 3

C++ is really nothing like Java. For example, functions don't have to be part of a class. You need to move the function main() so that it is outside the class.

class Race {
  // stuff
};

int main() {
  // stuff
}

Answer 4

You need a main function:

// The arguments are only needed if passing arguments to your program.
// You could just use `int main()`.
int main(int argc, char** argv)
{
    Race race;
    race.executeRace();
}

or so, without seeing your specific error.

Answer 5

You need a main() function to give the program a starting point:

int main()
{
     // whatever...
     // Maybe:

     Race race;

     race.main();
}

But it would probably make sense to have many of your methods be static methods since they don't rely on any instance members of the Race class.

Answer 6

It's complaining about main being undefined, and it's right. C and C++ require a standalone function named main which returns int. It is not sufficient to have a class with a method named main; the compiler only cares about the standalone one.

Another thing to remember is that the default visibility for members in a class type is private. Either change your class to use struct — that's pretty much the only difference between the two — or specify public visibility:

class Race {
public:
  void main() { ... }
};

Then you can call the main function from your class:

int main() {
  Race race;
  race.main();
  return EXIT_SUCCESS;
}