for (i = 0 ; i < rNumber-1 ; i++) {

    if xpos > 0 and xpos < rmax xpos = xpos+xdir else xpos = xpos+0
    if ypos > 0 and ypos < rmax ypos = ypos+ydir else ypos = ypos+0

    dir = irandom(1)
    if dir = 0 xdir = choose(-1,1) else xdir = 0
    if dir = 1 ydir = choose(-1,1) else ydir = 0

    if ds_grid_get(mainGrid, xpos+xdir, ypos+ydir) != 1 {
        ds_grid_set(mainGrid, xpos+xdir, ypos+ydir, 1)
        count +=1
        }