'C' Program: multidimensional array issue - c++

Question

Please help me figure this out, I have tested it and tested it and re-read and re-wrote for the past 11 hours and I give up. I found a working code that someone else wrote, but it still doesn't explain to me why his works and mine doesn't because the problem that I am having works on his but not on mine
Got it people, code edited for anyone who has had a similiar problem...
The original code that I had is here http://pastebin.com/h7fXHKzf
the problem I was having was that it kept hanging up on the if(board[x][y - 1] == '.') checks.
Spoke too soon....The program will sometimes crash...it's rare but has crashed 3x in a row before...most of the time when I run it everything works.
// Chapter 8 Programming Project #9
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 10
#define PATH_SIZE ((int) (sizeof(brd_path)))
#define ROW_SIZE ((int) (sizeof(board) / sizeof(board[0])))
int main(void)
{
char board[SIZE][SIZE] = {};
char brd_path[25] = {'B', 'C', 'D', 'E', 'F', 'G', 'H',
'I', 'J', 'K', 'L', 'M', 'N', 'O',
'P', 'Q', 'R', 'S', 'T', 'U', 'V',
'W', 'X', 'Y', 'Z'};
// 0 = Up, 1 = Down, 2 = Left, 3 = Right
bool path_dir_chk[4] = {false};
bool blocked = false;
unsigned short i, j, x = 0, y = 0;
// Generate a random number
srand((unsigned) time(NULL));
int dir = rand() % 4;
// Set all positions of board to '.'
for (x = 0; x < ROW_SIZE; x++) {
for (y = 0; y < ROW_SIZE; y++)
board[x][y] = '.';
}
x = 0;
y = 0;
board[0][0] = 'A';
// Generate the path
while (blocked != true && i != PATH_SIZE) {
for (i = 0; i < PATH_SIZE;) {
// Reset path_dir_chk values if empty
for (j = 0; j < 4; j++) {
if (board[x][y - 1] == '.')
path_dir_chk[0] = false;
if (board[x][y + 1] == '.')
path_dir_chk[1] = false;
if (board[x - 1][y] == '.')
path_dir_chk[2] = false;
if (board[x + 1][y] == '.')
path_dir_chk[3] = false;
}
// Check the direction and replace that char
switch (dir) {
case 0: if ((y - 1) >= 0 && board[x][y - 1] == '.') {
board[x][--y] = brd_path[i];
path_dir_chk[0] = true;
printf("I is now: %d\n", ++i);
} break;
case 1: if ((y + 1) >= 0 && board[x][y + 1] == '.') {
board[x][++y] = brd_path[i];
path_dir_chk[1] = true;
printf("I is now: %d\n", ++i);
} break;
case 2: if ((x - 1) >= 0 && board[x - 1][y] == '.') {
board[--x][y] = brd_path[i];
path_dir_chk[2] = true;
printf("I is now: %d\n", ++i);
} break;
case 3: if ((x + 1) >= 0 && board[x + 1][y] == '.') {
board[++x][y] = brd_path[i];
path_dir_chk[3] = true;
printf("I is now: %d\n", ++i);
} break;
}
// if all path's are true exit
if (path_dir_chk[0] == true &&
path_dir_chk[1] == true &&
path_dir_chk[2] == true &&
path_dir_chk[3] == true)
blocked = true;
// Reset the random direction
dir = rand() % 4;
}
}
// Print the board
for (x = 0; x < ROW_SIZE; x++) {
for (y = 0; y < ROW_SIZE; y++)
printf("%c ", board[x][y]);
printf("\n");
}
return 0;
}
OK I have made changes to reflect what I have so far, no it is printing 'I is now:' numbers 1 - 25 and then it starts over but it stops on 12 the second time around and freezes into some kind of loop
Below is the working code I found online, you can compare the two and see the similarity's but the lines of code on his that are exactly like mine do not work on mine.....
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define ROWS 10
#define COLS 10
int main (void)
{
int i, j, k, direction;
char board[ROWS][COLS];
const char letters[] = {'A', 'B', 'C', 'D', 'E', 'F',
'G', 'H', 'I', 'J', 'K', 'L',
'M', 'N', 'O', 'P', 'Q', 'R',
'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z'};
srand ((unsigned) time(NULL));
for (i = 0; i < ROWS; i++)
for (j = 0; j < COLS; j++)
board[i][j] = '.';
i = 0;
j = 0;
k = 1;
//set array[0][0] to first element
board[i][j] = letters[0];
while (k < 26) {
direction = rand() % 4;
if (board[i][j] == '.')
board[i][j] = letters[k++];
if ((board[i][j + 1] != '.' || j == ROWS - 1 )&&
(board[i + 1][j] != '.' || i == COLS -1) &&
(board[i - 1][j] != '.' || i == 0) &&
(board[i][j - 1] != '.' || j == 0))
break;
switch (direction) {
case 0: if (j < ROWS - 1 && board[i][j + 1] == '.'){ //move right
j++;
break; }
case 1: if (i < COLS -1 && board[i + 1][j] == '.') { //move down
i++;
break; }
case 2: if (i > 0 && board[i - 1][j] == '.'){ //move up
i--;
break; }
case 3: if (j > 0 && board[i][j - 1] == '.') { //move left
j--;
break; }
}
}
for (i = 0; i < ROWS; i++) {
for (j = 0; j < COLS; j++)
printf ("%4c", board[i][j]);
printf ("\n");
}
return 0;
}

Answer 1

You aren't setting x and y back to 0 after this code
for (x = 0; x < ROW_SIZE; x++) {
for (y = 0; y < ROW_SIZE; y++)
board[x][y] = '.';
}
Thus x and y will start at 10. Also you aren't range checking x and y, which means that x and y might wander off the board.
This code
if ((board[x][y - 1] != '.' || y - 1 < 0) &&
(board[x][y + 1] != '.' || y + 1 > ROW_SIZE) &&
(board[x - 1][y] != '.' || x - 1 < 0) &&
(board[x + 1][y] != '.' || x + 1 > ROW_SIZE))
should be this
if ((y - 1 < 0 || board[x][y - 1] != '.') &&
(y + 1 >= ROW_SIZE || board[x][y + 1] != '.') &&
(x - 1 < 0 || board[x - 1][y] != '.') &&
(x + 1 >= ROW_SIZE || board[x + 1][y] != '.'))
There are two subtle differences.
First y+1 and x+1 are not allowed to be equal to ROW_SIZE, since ROW_SIZE is 10, but the valid array indices are 0 to 9.
Second, order is important. When evaluating a logical OR, the left side is evaluated first, and if it's true, then the right side is not evaluated. This is important, since on some machines, even reading outside of the array bounds will cause a crash.

Answer 2

for (x = 0; x < ROW_SIZE; x++) {
for (y = 0; y < ROW_SIZE; y++)
board[x][y] = '.';
}
After the initialization you are not resetting the value of x and y. While value of X= ROW_SIZE, you are trying to access board[x + 1][y] and board[x][y + 1].
x = 0;
y = 0;

Answer 3

Thanks user3386109 your input was invaluable as was the rest of y'alls help I appreciate it, the working code is below :)
// Chapter 8 Programming Project #9
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 10
#define PATH_SIZE 25
#define ROW_SIZE ((int) (sizeof(board) / sizeof(board[0])))
int main(void)
{
char board[SIZE][SIZE];
// 0 = Up, 1 = Down, 2 = Left, 3 = Right
unsigned short i = 0, x, y;
// Generate a random number
srand((unsigned) time(NULL));
int dir = rand() % 4;
// Set all positions of board to '.'
for (x = 0; x < ROW_SIZE; x++) {
for (y = 0; y < ROW_SIZE; y++)
board[x][y] = '.';
}
x = 0;
y = 0;
board[0][0] = 'A';
// Generate the path
for (i = 0; i < PATH_SIZE;) {
// Check that the last character has not been cornered
if ((board[x][y - 1] != '.' || y - 1 < 0) &&
(board[x][y + 1] != '.' || y + 1 > ROW_SIZE) &&
(board[x - 1][y] != '.' || x - 1 < 0) &&
(board[x + 1][y] != '.' || x + 1 > ROW_SIZE))
break;
// Check the direction and replace that char
switch (dir) {
case 0: if ((y - 1) >= 0
&& board[x][y - 1] == '.') {
board[x][--y] = i + 'B';
++i;
} break;
case 1: if ((y + 1) < ROW_SIZE
&& board[x][y + 1] == '.') {
board[x][++y] = i + 'B';
++i;
} break;
case 2: if ((x - 1) >= 0
&& board[x - 1][y] == '.') {
board[--x][y] = i + 'B';
++i;
} break;
case 3: if ((x + 1) < ROW_SIZE
&& board[x + 1][y] == '.') {
board[++x][y] = i + 'B';
++i;
} break;
default: if (board[x][y] == '.')
board[x][y] = i + 'B';
break;
}
// Reset the random directions
dir = rand() % 4;
}
// Print the board
for (x = 0; x < ROW_SIZE; x++) {
for (y = 0; y < ROW_SIZE; y++)
printf("%4c ", board[x][y]);
printf("\n");
}
return 0;
}