You can think of your grid array as a contiguous piece of memory. I would do: bzero(grid, sizeof(int) * COLS); bzero(grid + COLS * (ROWS - 1), sizeof(int)

You can think of your grid array as a contiguous piece of memory. I would do: bzero(grid, sizeof(int) * COLS); bzero(grid + COLS * (ROWS - 1), sizeof(int) * COLS); for (int i=1; i < ROWS-1; i++) { *(grid + (i * COLS)) = 0; /* set left col to 0 */ *(grid + (i * COLS) + COLS - 1) = 0; /* set right col to 0 */ }