The Screen Is a Grid

So far text has landed wherever the last PRINT left off. Now you take charge of where. The Spectrum’s screen is a grid — 32 columns across, 24 rows down — and PRINT AT puts text at any cell you name.

Milestone 1 — place a word

  10 CLS
  20 PRINT AT 10,13;"Here"

PRINT AT 10, 13; "Here" prints at row 10, column 13 — roughly the middle. The order is row first, then column (down, then across), and both count from 0 at the top-left.

Milestone 2 — address the whole grid

Give the corners and the centre their own PRINT ATs and the grid comes into focus:

1   10 CLS
2−Removed:   20 PRINT AT 10,13;"Here"
2+Added:   20 PRINT AT 0,0;"top-left"
3+Added:   30 PRINT AT 0,22;"top-right"
4+Added:   40 PRINT AT 21,0;"bottom-left"
5+Added:   50 PRINT AT 10,13;"middle"

Row 0 is the top, row 21 near the bottom (the lowest two rows are kept for the input area), column 0 the left edge, column 31 the right. Each label lands exactly where its numbers put it.

Milestone 3 — the title card finds its spot

Back to the title card. In Unit 3 it printed from the top-left; now you can place it where you want — centred, like a real game’s opening screen:

  10 CLS
  20 PRINT AT 8,11;"MEET BASIC"
  30 PRINT AT 10,7;"a Spectrum primer"

To centre a line, leave equal space each side: MEET BASIC is 10 characters, so starting at column 11 leaves 11 columns either side of the 32.

When it doesn’t work

• The text landed in the wrong place. AT is row, then column — AT 10, 13 is row 10, column 13, not the other way round. A common slip.
• Integer out of range. A row above 21 or a column above 31 is off the grid. Keep rows 0–21 and columns 0–31.
• It printed at the top-left anyway. Check the punctuation: PRINT AT row, col; — a semicolon after the position, before the text.

Before and after

You started with text landing wherever the last PRINT left off and finished placing it anywhere on a 32-by-24 grid — corners, centre, a centred title. The idea underneath: PRINT AT row, column addresses the screen as a grid, counting from 0 at the top-left.

Try this

• Centre your name. Work out the column that centres it and place it mid-screen.
• A border of dots. Use a FOR loop and PRINT AT to run a row of dots along the top.
• Stack a menu. Place three options at rows 8, 10 and 12, all at the same column.

What you’ve learnt

• The screen is a grid: 32 columns, 24 rows, addressed from 0 at the top-left.
• PRINT AT row, column; "text" places text exactly — row first, then column.
• The print area is rows 0–21; the lowest two rows are the input area.
• Centre a line by leaving equal columns on each side.

What’s next

The title card has a place — but it’s still grey on grey. In Unit 10 we bring colour: INK, PAPER, BORDER, and a loop that paints the title in every colour at once.