Screen 13 will be used within this tutorial. Screen 13 has a resolution of 320 x 200. This tutorial will show the screen coordinates.

The tutorial in the old QBasic Tutorial Series, regarding coordinates, was wrong. The old tutorial had screen coordinates of:

(0, 0)
(0, 200)
(320, 200)
(320, 0)

Since the starting coordinate is 0,0 that means that the math equation of n - 1 needs to be used. So, the farthest coordinate for Screen 13 is (320 - 1, 200 - 1) which gives us (319, 199).

The correct coordinates for each corner, of Screen 13, is:

(0, 0)
(0, 199)
(319, 199)
(319, 0)

PSET will place a pixel at a specified coordinate and color.

Code Download
QBT26_1.BAS - Incorrect Coordinates
QBT26_2.BAS - Correct Coordinates