Accessing out of bounds cells in a 2D array - c

Question

I can't really see what's wrong with my check neighbors function in my game of life. It checks all the 8 neighbours then depending on the living count assigns the cell being checked to living or dead, then updates the board.
void check_neighbours (int board[][COL])
{
int living = 0, i, j, k, l;
int new_board[ROW][COL];
for (i = 0; i < ROW; i++)
{
for (j = 0; j < COL; j++)
{
if ((board[i + 1 % ROW][j % COL]) == '#')
{
living++;
}
if ((board[i - 1 % ROW ][j % COL]) == '#')
{
living++;
}
if ((board[i % ROW][j + 1 % COL]) == '#')
{
living++;
}
if ((board[i % ROW][j - 1 % COL]) == '#')
{
living++;
}
if ((board[i + 1 % ROW][j + 1 % COL]) == '#')
{
living++;
}
if ((board[i - 1 % ROW ][j + 1 % COL ]) == '#')
{
living++;
}
if ((board[i + 1 % ROW ][j - 1 % COL ]) == '#')
{
living++;
}
if ((board[i - 1 % ROW ][j - 1 % COL ]) == '#')
{
living++;
}
if (living == 3)
{
new_board[i][j] = '#';
}
if (living <= 2)
{
new_board[i][j] = '-';
if (living < 3)
{
new_board[i][j] = '-';
}
}
}
for (k = 0; k < ROW; k++)
{
for (l = 0; l < COL; l++)
{
board[k][l] = new_board[k][l];
}
}
}
}
edit: Added parentheses but still prints the same

Answer 1

Try sticking some brackets into your math:
board[(i + 1) % ROW]
is much safer than
board[i + 1 % ROW]

Answer 2

Test edge conditions before doing the living count.
for (i = 0; i < ROW; i++) {
for (j = 0; j < COL; j++) {
int living = 0;
for (int drow = -1; drow <= 1; drow++) {
int row = i+drow;
if (row < 0 || row >= ROW) continue; // over the edge
for (int dcol = -1; dcol <= 1; dcol++) {
int col = j+dcol;
if (col < 0 || col >= COL) continue; // over the edge
if (row==0 && col==0) continue;
if (board[row][col] == '#') {
living++;
}
} // endfor dcol
} // endfor drow
// This section may need review - GOL rules are unclear in post -see below
if (living == 3) {
new_board[i][j] = '#';
}
...
} // endfor j
} // endfor i
If rules follow:
Any live cell with fewer than two live neighbors dies, as if caused by under-population.
Any live cell with two or three live neighbors lives on to the next generation.
Any live cell with more than three live neighbors dies, as if by over-population.
Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction.
#define ALIVE ('#')
#define DEAD ('-')
#define POP_MIN 2
#define POP_MAX 3
#define POP_REPRO 3
new_board[i][j] = board[i][j];
if (board[i][j] == ALIVE) {
if (living < POP_MIN) new_board[i][j] = DEAD;
else if (living > POP_MAX) new_board[i][j] = DEAD;
} else {
if (living == POP_REPRO) new_board[i][j] = ALIVE;
}

Answer 3

Isn't this:
board[i + 1 % ROW]
going out of bounds? Try fixing these issues.
As Paul R suggested, you could use parentheses, in order to catch up with the higher precedence of % operator in comparison to the + operator. So change the code to this:
board[(i + 1) % ROW]
Assuming ROW = 5 and i = 4, you get:
(4 + 1) % 5 = 0 // yeah!
4 + 1 % 5 = 5 // oh dear...