Code not working :-(

I'm think you want this?

Graphics 800,600
SetBuffer BackBuffer()


Global world_x = 0
Global world_y = 0
Global world_width = 800
Global world_height = 600
Global grid_x = 0
Global grid_y = 0
Global grid_width = 9
Global grid_height = 9
Global tile_size = 50
Global cursor_x = 0 
Global cursor_y = 0


Dim world(world_width-1,world_height-1)

For x=0 To world_width-1
	For y=0 To world_height-1
		world(x,y)=0
	Next
Next



While Not KeyHit(1)
Cls

	user_control
	draw_world
	draw_grid
	
	Flip
	
Wend



Function draw_grid()

	For x=0 To grid_width
		For y=0 To grid_height
			Rect grid_x+x*tile_size,grid_y+y*tile_size,tile_size,tile_size,0
		Next
	Next

	Color 0,0,255
	Rect grid_x+cursor_x*tile_size,grid_y+cursor_y*tile_size,tile_size,tile_size,0
	Color 255,255,255

End Function 




Function draw_world()
	
	For x1=0 To grid_width
		For y1=0 To grid_height
			
			;For x2=0 To 10
				;For y2=0 To 10
					If world(x1,y1)=1 Then 
						Oval grid_x+x1*tile_size,grid_y+y1*tile_size,5,5
					EndIf
				;Next
			;Next
			
		Next
	Next
	
End Function



Function user_control()

	If KeyHit(205) And cursor_x<grid_width Then cursor_x = cursor_x + 1
	If KeyHit(203) And cursor_x>0 Then cursor_x = cursor_x - 1
	If KeyHit(200) And cursor_y>0 Then cursor_y = cursor_y - 1
	If KeyHit(208) And cursor_y<grid_height Then cursor_y = cursor_y + 1
	
	If KeyHit(57) Then world(cursor_x,cursor_y)=1
	
End Function