C++: array index is not increasing

Question

I want to make a simple game of 3 players, each player moves in a block depending of the random function from 1 to 6 blocks each time, when first player has been moved the second player start and then then the third player. To do that I increase the index of an array rach time a player finish its move.

My problem is that the indexer seems no to been increased, and it stacks in the player 1 even if I increase it. I have exactly the same code in C# and it works well!

Here is the code in C++.

int main ()
{
        string namesofplayers[] = {"one","two","three"};

        int movementofplayers[] = {0,0,0}; // start position of players is 
        int gamesize = 32; //32 blocks-steps of game
        int random;
        int y = 0;

        a:

        y++;
        if (y >= 3) 
        {
            y = 0;
        }
        cout << "it's" << namesofplayers[y] << "turn to play";
        int R = (rand() % 6 + 1);
        cout << "player " << namesofplayers[y] << " moves to block" << R << endl;
        movementofplayers[y] += random;
        cout << movementofplayers[y];


        if (movementofplayers[y] < gamesize)
        {
             goto a;
        }
        else 
        { 
              cout << "Player " << namesofplayers[y] << " wins the game" << endl;
        }
}

Answer 1

On the off chance of doing your work, I took the liberty to write up an alternative implementation which fixes some of the problems your former code had and also produces more readable output. I also threw out the one-liners because they drive me crazy, but that's personal preference. Also, I tend to explicitly qualify symbols from the standard library using the appropriate scope.

1. Get rid of goto. You can browse SO and the web for multiple reasons why not to use an explicit jump like that. Just use a loop

2. Fix the missing initial seed for the pseudo-random number generator. If you set a varying seed, i.e. by invoking it with some variable value (e.g. time(nullptr) ), you'll always get the same succession of "random" values - with each program invocation.

3. Fix the use of the variable random. You tried to add some garbage-initialized value random to movementofplayers[y]. Interestingly, g++-4.7 seems to ensure that the variable is set to 1 before being used in the arithmetic op. However, the correct variable you need is R.

4. Return a well defined value from main().

I hope the code still does what you intended it to do:

#include <string>
#include <iostream>

int main ()
{
  srand(time(NULL));
  std::string namesofplayers[] = {"one","two","three"};

  int movementofplayers[] = {0,0,0}; // start position of players is
  int gamesize = 32;                 //32 blocks-steps of game
  int y = 1;

  while(movementofplayers[y] < gamesize)
  {
    if (y >= 3)
    {
      y = 0;
    }

    std::cout << "it's " << namesofplayers[y] << " turn to play" << std::endl;
    int R = (rand() % 6 + 1);
    std::cout << "player " << namesofplayers[y] << " moves to block " << R << std::endl;
    movementofplayers[y] += R;
    std::cout << "movements of player " << namesofplayers[y] <<": " << movementofplayers[y] << std::endl;

    y++;
  }

  std::cout << "Player " << namesofplayers[y] << " wins the game" << std::endl;

  return 0;
}

Answer 2

Here is how I would do it.

Added seeding the random number generator so you don't get the same game every time.

Added a constant for number of players to get rid of the magic number and also make it easier to expand the number of players if desired.

Got rid of the goto. Although it is possible to use goto in a reasonable way it is prone to accidental misuse, makes the code harder to follow, and makes people angry. :)

I tweaked the output and names a bit just to make it a little easier for me to test. In doing so I corrected an issue where it said the player moved to block R which was their roll for that turn, not their actual position in the game.

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

int main()
{
    std::srand(static_cast<unsigned int>(std::time(0)));

    const int gamesize = 32;
    const int num_players = 3;
    const std::string namesofplayers[num_players] = {"1", "2", "3"};
    int movementofplayers[num_players] = {0, 0, 0};

    int current_player = 0;
    for(;;) //Loop forever, the game logic will exit the loop when a winner is found
    {
        const int roll = rand() % 6 + 1;
        movementofplayers[current_player] += roll;

        std::cout << "Player " << namesofplayers[current_player] << " rolls a " << roll << " and moves to block " << movementofplayers[current_player] << std::endl;
        //Check if they won and if so, end the game
        if(movementofplayers[current_player] >= gamesize)
        {
            std::cout << "Player " << namesofplayers[current_player] << " wins the game!" << std::endl;
            break;
        }
        current_player = (current_player + 1) % num_players;
    }
    return 0;
}