My version for the game of Fifteen

fifteen.c

/**
 * 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 * Note that usleep is obsolete, but it offers more granularity than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

// 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);
bool isEven(int num);

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;
    }

    // greet user with instructions
    greet();

    // initialize the board
    init();

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

    // 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 in a log file
        for (int i = 0; i < d; i++)
        {
            for (int 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();

        // 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)
{
    // maximum number to print
    int tilenum = d*d;
    for (int i = 0; i < d; i++)
    {
        for (int j = 0; j < d; j++)
        {
            // fill tiles in descending order
            board[i][j] = --tilenum;
        }
    }
    // swap "last two" only if d is even
    if (isEven(d))
    {
        board[d - 1][d - 3] = 1;
        board[d - 1][d - 2] = 2;
    }
}


/**
 * Prints the board in its current state.
 */
void draw(void)
{
    printf ("\n");
    for (int i = 0; i < d; i++)
    {
        for (int j = 0; j < d; j++)
        {
            if (board[i][j] == 0)
            {
                // blank title
                printf("%3s", " _ ");
            }
            else
            {
                printf("%2d", board[i][j]);
                if (j < d - 1)
                {
                    printf(" ");
                }
            }
        }
        printf("\n\n");
    }
}

/**
 * If tile borders empty space, moves tile and returns true, else
 * returns false. 
 */
bool move(int tile)
{
    // move through the 2-d array as usual
    for (int i = 0; i < d; i++)
    {
        for (int j = 0; j < d; j++)
        {
            // Locate our tile, then check for blank tile to the right, left, above and below
            if (board[i][j] == tile)
            {
                // blank to the right?
                if ((j + 1 <= d - 1) && (board[i][j + 1] == 0))
                {
                    board[i][j + 1] = tile;
                    board[i][j] = 0;
                    return true;
                }
                
                // blank to the left?
                if ((j - 1 >= 0) && (board[i][j - 1] == 0))
                {
                    board[i][j - 1] = tile;
                    board[i][j] = 0;
                    return true;
                }
        
                // blank above?
                if ((i - 1 >= 0) && (board[i - 1][j] == 0))
                {
                    board[i - 1][j] = tile;
                    board[i][j] = 0;
                    return true;
                }

                // blank below?
                if ((i + 1 <= d - 1) && (board[i + 1][j] == 0))
                {
                    board[i + 1][j] = tile;
                    board[i][j] = 0;
                    return true;
                }
            }
        }
    }
    return false;
}

/**
 * Returns true if game is won (i.e., board is in winning configuration), 
 * else false.
 */
bool won(void)
{
    // if sorted, blank tile must be the last one, if not, don't waste time and exit false
    if ((board[d - 1][d - 1]) != 0)
    {
        return false;
    }

    // first number must be 1
    int num = 1;
    
    // move through the 2-d array as usual
    for (int i = 0; i < d; i++)
    {
        for (int j = 0; j < d; j++)
        {
            // if we reached last element and we haven't exit so far, then we won
            if ((i == (d - 1)) && (j == (d - 1)))
            {
                return true;
            }
            if (num != board[i][j])
            {
                return false;
            }
            num++;
        }
    }
    return true;
}

/**
 * Returns true if num is even, false if it is odd 
 */
 bool isEven(int num)
 {
     if (num % 2 == 0)
     {
         return true;
     }
     else
     {
         return false;
     }
 }