C - check matrix[x][y] positions around - c

Question

I've a matrix with size 7x7 that represents a game board. When a player makes a move, the program has to check the positions around the coordinates where the piece is, in order to detect another piece aside.
I use this function:
int check_position(COORDINATES coordinates, char board[7][7]) {
int result = -1;
if (board[coordinates.x][coordinates.y] != 'O' && board[coordinates.x-1][coordinates.y] != 'O' && board[coordinates.x][coordinates.y-1] != 'O' && board[coordinates.x+1][coordinates.y] != 'O' && board[coordinates.x][coordinates.y+1] != 'O' && board[coordinates.x-1][coordinates.y-1] != 'O' && board[coordinates.x+1][coordinates.y+1] != 'O' && board[coordinates.x-1][coordinates.y+1] != 'O' && board[coordinates.x+1][coordinates.y-1] != 'O') {
result = 1;
}
return result;
}
The first parameter are the coordinates of the player's piece as a struct, with members x and y. The second parameter is the board array.
The if statement doesn't work to well, and I don't know which alternative can I take.
Can you help me? Thanks!

Answer 1

You forgot about your coordinates overflowing at the borders. You can either test for this, or:
Hint: Make the array two rows and columns larger than the board and fill the border with "empty" marker. The active board will the have coordinates 1...7 This way your coordinates cannot wrap (1 - 1 and 7 + 1 are still within the array) and you do not have to care about the borders.
Note: If you just want to return a boolean value, it would be better to use stdbool.h and return a bool result. That way, the caller can directly use that function as a condition:
#include <stdbool.h>
...
bool check_position(COORDINATES coordinates, const char board[9][9]) {
int x = coordinates.x - 1
for ( int xc = 0 ; xc < 3 ; xc++ ) {
int y = coodinates.y - 1;
for ( int yc = 0 ; yc < 3 ; yc++ ) {
if ( board[x][y] != '0' )
return true;
y++;
}
x++;
}
return false;
}
Note: as you only need one one non-empty field, you can terminate instantly if you found one. That is identical to the multiple conditions. Of course, that also works for your original int result.
Note2: I modified the type of board to being const, as it is not changed inside the function.

Answer 2

You could also solve the edge overflow like this. Edit improved after discussion with #Olaf
#define BOARD 7
int check_position(COORDINATES coordinates, char board[BOARD][BOARD]) {
int result = -1;
int left = coordinates.x == 0 ? 0 : coordinates.x - 1;
int top = coordinates.y == 0 ? 0 : coordinates.y - 1;
int right = coordinates.x == BOARD-1 ? coordinates.x : coordinates.x + 1;
int bottom = coordinates.y == BOARD-1 ? coordinates.y : coordinates.y + 1;
if (board[left] [top] != 'O' &&
board[coordinates.x][top] != 'O' &&
board[right] [top] != 'O' &&
board[left] [coordinates.y] != 'O' &&
board[coordinates.x][coordinates.y] != 'O' &&
board[right] [coordinates.y] != 'O' &&
board[left] [bottom] != 'O' &&
board[coordinates.x][bottom] != 'O' &&
board[right] [bottom] != 'O' && )
{
result = 1;
}
return result;
}