JT1 JT1 - 3 months ago 8
C Question

C, Initialize 2D array with a for loop

I am having trouble populating my 2d array with values. A ton of examples have a static array, however, I'm using a for loop to populate it. This is what I would like my code to do:


  • The second argument is d, say the user enters 3, then:

  • a 3x3 array is created.

  • The array would store all values from 8 to 0.

  • It prints the array like this to the terminal:



8 7 6

5 4 3

2 1 0


  • If the user passes in a 4, then a 4x4 array would be created

  • It would print this to the console:



15 14 13 12

11 10 9 8

7 6 5 4

3 2 1 0

/**
* fifteen.c
*
* Computer Science 50
* Problem Set 3
*
* Implements the 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 [MIN,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* Note that usleep is obsolete, but it offers more granularity than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>

// board's minimal dimension
#define MIN 3

// board's maximal dimension
#define MAX 9

// board, whereby board[i][j] represents row i and column j
int board[MAX][MAX];

// board's dimension
int d;

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

int main(int argc, string argv[])
{
// greet player
greet();

// ensure proper usage
if (argc != 2)
{
printf("Usage: ./fifteen [3-9]\n");
return 1;
}

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

// initialize the board
init();

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

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

// saves the current state of the board (for testing)
save();

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

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

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

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

// that's all folks
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("GAME OF FIFTEEN\n");
//usleep(2000000);
}

/**
* Initializes the game's board with tiles numbered 1 through d*d - 1,
* (i.e., fills board with values but does not actually print them),
* whereby board[i][j] represents row i and column j.
*/
void init(void)
{
// TODO
// represent board in 2D integer array
// int board [MAX][MAX]
// int d
// size of board. d <= MAX
// board [i][j] represents the element at row i and col j
// starts in descending order
// if number of tiles is odd, swap 2 and 1

/**
take d and print board with dxd dimensions
loop through x to go up to d-1 (i.e. 4x4 board = 16, values will be 15 to 1)
*/

//initialize array
int numbers[d][d];

//print the array size
printf("Array size:%d\n", d);

//variable i, j
int i;
int j;

// board's numbering
int s = (d*2)-1;
int countarray[d];
int count;
for (count = s; count > 0; count--)
{
countarray[count]=count;
}
printf("Start of board's numbering: %d\n", s);

//assign values to array with loop

for (i = 0; i < d; i++)
{
for ( j = 0; j < d; j++)
{
numbers[i][j] = 0;
numbers[i][j] = countarray[count];
printf("numbers[%d][%d] = %d \n", i, j, numbers[i][j]);
}
}

//print a number from the array
printf("The 4th integer of the array is: %d\n", numbers[3][3]);
printf("Value of d: %d\n", d);
for (int x = 0; x < d; x++){
for (int y = 0; y < d; y++){
// print the array value [ x, y ]
printf("%d", numbers[x][y]);
printf(" ");
}
// print a new line here
printf("\n");
}
}

/**
* Prints the board in its current state.
*/
void draw(void)
{
// TODO
// print current state of the board
// print a blank space fore single digit #s
// printf("%2d", board[i][j]);

/**
for each row
for each value in row
print value and space
print new line
*/


}

/**
* If tile borders empty space, moves tile and returns true, else
* returns false.
*/
bool move(int tile)
{
// TODO
return false;
}

/**
* Returns true if game is won (i.e., board is in winning configuration),
* else false.
*/
bool won(void)
{
// TODO
return false;
}

/**
* Saves the current state of the board to disk (for testing).
*/
void save(void)
{
// log
const string log = "log.txt";

// delete existing log, if any, before first save
static bool saved = false;
if (!saved)
{
unlink(log);
saved = true;
}

// open log
FILE* p = fopen(log, "a");
if (p == NULL)
{
return;
}

// log board
fprintf(p, "{");
for (int i = 0; i < d; i++)
{
fprintf(p, "{");
for (int j = 0; j < d; j++)
{
fprintf(p, "%i", board[i][j]);
if (j < d - 1)
{
fprintf(p, ",");
}
}
fprintf(p, "}");
if (i < d - 1)
{
fprintf(p, ",");
}
}
fprintf(p, "}\n");

// close log
fclose(p);
}


With an argument of 3, it correctly prints a 3x3 array to the terminal. However, all 9 values in the array are 134517847. I would appreciate any help, thank you.

Answer

In the inner loop the wrong variable x is being incremented. Should be y++ not x++.

 for (int x = 0; x < d; x++){
    for (int y = 0; y < d; x++){
                           ^^^

The loop needs to iterate for count == 0. Change the condition from > to >=.

    for (count = s; count >= 0; count--)
    {
        countarray[count]=count;
    }

s is initialised to

  int s = (d*2)-1;

but should that not be d*d-1 ?

  int s = (d*d)-1;

In the loop that initialises the numbers array, count is not initialised nor decremented. I'm guessing you require something like this:

count = s;
for (i = 0; i < d; i++)
{
        for ( j = 0; j < d; j++)
        {
            numbers[i][j] = countarray[count--];
            printf("numbers[%d][%d] = %d \n", i, j, numbers[i][j]);
        }
}
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