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I'm fed up of checking the fault in my code and when I'm playing the game it disappears some numbers like in first step when I try to swap the blank space with 1 I get two blank spaces and 1 gets disappear. This type of thing is happening in some places don't know why ?

/**
 * fifteen.c
 *
 * Computer Science 50
 * Problem Set 3
 *
 * Implements Game of Fifteen (generalized to d x d).
 *
 * Usage: fifteen d
 *
 * whereby the board's dimensions are to be d x d,
 * where d must be in [DIM_MIN,DIM_MAX]
 *
 * Note that usleep is obsolete, but it offers more granularity than
 * sleep and is simpler to use than nanosleep; `man usleep` for more.
 */

#define _XOPEN_SOURCE 500

#include <cs50.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// constants
#define DIM_MIN 3
#define DIM_MAX 9
#define BLANK 0

// board
int board[DIM_MAX][DIM_MAX];

// dimensions
int d;

// prototypes
void clear(void);
void greet(void);
void init(void);
void draw(void);
bool move(int tile);
bool won(void);

int main(int argc, string argv[])
{
    // ensure proper usage
    if (argc != 2)
    {
        printf("Usage: fifteen d\n");
        return 1;
    }

    // ensure valid dimensions
    d = atoi(argv[1]);
    if (d < DIM_MIN || d > DIM_MAX)
    {
        printf("Board must be between %i x %i and %i x %i, inclusive.\n",
            DIM_MIN, DIM_MIN, DIM_MAX, DIM_MAX);
        return 2;
    }

    // open log
    FILE* file = fopen("log.txt", "w");
    if (file == NULL)
    {
        return 3;
    }

    // greet user with instructions
    greet();

    // initialize the board
    init();

    // accept moves until game is won
    while (true)
    {
        // clear the screen
        clear();

        // draw the current state of the board
        draw();

        // log the current state of the board (for testing)
        for (int j, i = 0; i < d; i++)
        {
            for (j = 0; j < d; j++)
            {
                fprintf(file, "%i", board[i][j]);
                if (j < d - 1)
                {
                    fprintf(file, "|");
                }
            }
            fprintf(file, "\n");
        }
        fflush(file);

        // check for win
        if (won())
        {
            printf("ftw!\n");
            break;
        }

        // prompt for move
        printf("Tile to move: ");
        int tile = GetInt();

        // quit if user inputs 0 (for testing)
        if (tile == 0)
        {
            break;
        }

        // log move (for testing)
        fprintf(file, "%i\n", tile);
        fflush(file);

        // move if possible, else report illegality
        if (!move(tile))
        {
            printf("\nIllegal move.\n");
            usleep(500000);
        }

        // sleep thread for animation's sake
        usleep(500000);
    }

    // close log
    fclose(file);

    // success
    return 0;
}

/**
 * Clears screen using ANSI escape sequences.
 */
void clear(void)
{
    printf("\033[2J");
    printf("\033[%d;%dH", 0, 0);
}

/**
 * Greets player.
 */
void greet(void)
{
    clear();
    printf("WELCOME TO GAME OF FIFTEEN\n");
    usleep(2000000);
}

/**
 * Initializes the game's board with tiles numbered 1 through d*d - 1
 * (i.e., fills 2D array with values but does not actually print them).  
 */
void init(void)
{
    int count = d*d - 1;
    for (int i = 0; i < d; i++)
    {
        for ( int j = 0; j < d; j++, count--)
        {
            board[i][j] = count;
        }
    }
    if (board[d-1][d-1] == 0)
    {
        board[d-1][d-1] = BLANK;
    }
    if (d % 2 == 0)
    {
        int temp = board[d-1][d-2];
        board[d-1][d-2] = board[d-1][d-3];
        board[d-1][d-3] = temp;
    }
}

/**
 * Prints the board in its current state.
 */
void draw(void)
{
    printf("\n\n");
    for (int i = 0; i < d; i ++)
    {
        for ( int j = 0; j < d; j ++)
        {
            if (board[i][j] == BLANK && j != d-1)
            {
                printf("   _");
            }
            else if (board[i][j] == BLANK && j == d-1)
            {
                printf("   _\n");
            }
            else if (j == d - 1)
            {
                printf("  %2d\n", board[i][j]);
            }
            else 
            {
                printf("  %2d", board[i][j]);
            }
        }
        printf("\n");        
    }

}

/**
 * If tile borders empty space, moves tile and returns true, else
 * returns false. 
 */
bool move(int tile)
{
    for (int i = 0; i < d; i ++)
    {
        for ( int j = 0; j < d; j ++)
        {
            if (board[i][j] == tile)
            {
                if (board[i + 1][j] == BLANK)
                {
                    board[i][j] = BLANK;
                    board[i + 1][j] = tile;
                    return true;
                }
                if (board[i - 1][j] == BLANK)
                {
                    board[i][j] = BLANK;
                    board[i - 1][j] = tile;
                    return true;
                }
                if (board[i][j + 1] == BLANK)
                {
                    board[i][j] = BLANK;
                    board[i][j+1] = tile;
                    return true;
                }
                if (board[i][j - 1] == BLANK)
                {
                    board[i][j] = BLANK;
                    board[i][j-1] = tile;
                    return true;
                }
            }
        }
    }

    return false;
}

/**
 * Returns true if game is won (i.e., board is in winning configuration), 
 * else false.
 */
bool won(void)
{
    int total = 1;
    for (int i = 0; i < d; i ++)
    {
        for (int j = 0; j < d; j++)
        {
            if (board[i][j] == total)
            {
                total++;

                if (total == d * d)
                {
                    return true;
                }
            }
            else
            {
                return false;
            }

        }
    }
    return false;
}

1 Answer 1

1

Because you're going off the edge of the board! Plug the following into your move() function: d=3, i=2, j=2. Which element in board[][] are you testing when you look at board[i + 1][j]?

6
  • I put "if statement" there...shouldn't this "board[i+1][j]" be ignored if there is no element Commented Feb 23, 2016 at 11:25
  • Thanks anyways it worked....but I'm just curious why if statement is not ignoring if there is no element ? and what exactly is happening there if "if statement" does not ignore ? Commented Feb 23, 2016 at 11:33
  • Having the exact same problem here... andi still have the same inquiries. Why isn`t the "if" being ignored if the tile is not in that position? And how did you solve the problem anyway?
    – user10927
    Commented Feb 28, 2016 at 12:07
  • If you have the "exact same problem" and the same code, that code is accessing data outside of the array. C doesn't do validation of array indexes and will allow this. The data that you're comparing in these invalid array elements are actually data contained in other variables, random garbage data, or data belonging to other programs. Since you're looking for a 0, it's entirely possible to pass the if test in the code, make the swap and corrupt data on both sides of the trade.
    – Cliff B
    Commented Feb 28, 2016 at 16:19
  • I was very surprised to see how many others besides myself attempted to use this same technique of checking against a condition we believed would never be true which was that there won't be data in that part of the array (board[j + 1] in the case of the blank being furthest to the right). I thought there would be a segmentation fault when I first tried this but indeed, if at the time of your move there is no garbage data there, your condition won't be met and the game will appear to work fine.
    – user11211
    Commented Apr 4, 2016 at 1:35

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