Sinclair ZX Spectrum Framework Beginner

Text Utilities (BASIC)

Centre text on any row and clear rows — two tiny subroutines used in every BASIC game.

Taught in BASIC Game 1, Unit 1 textcentreclearprintbasicutility

Overview

Two subroutines that appear in every Spectrum BASIC game. Centre text calculates the column from the string length and prints at the midpoint. Clear row overwrites a row with spaces. Together they handle all status messages, titles, and feedback text without manual column counting.

Code

  10 REM Text utilities
  20 REM Pattern: reusable across games
  30 REM
  40 REM Centre text:
  50 REM   LET r=10: LET t$="Hello": GO SUB 3000
  60 REM   Set INK, BRIGHT, FLASH etc before calling
  70 REM
  80 REM Clear row (cols 2-29, inside a frame):
  90 REM   LET r=10: GO SUB 3100
 100 REM
3000 REM === Centre text t$ on row r ===
3010 PRINT AT r,(32-LEN t$)/2;t$
3020 RETURN
3100 REM === Clear row r (cols 2-29) ===
3110 PRINT AT r,2;"                            "
3120 RETURN

Trade-offs

AspectDetail
SpeedTwo PRINT AT calls — negligible overhead
Memory4 lines of code total
LimitationClear row assumes cols 1-30 (inside a frame). Adjust for full-width
FlexibilitySet INK, BRIGHT, FLASH before calling — the subroutine inherits them

When to use: Every game. Title screens, feedback messages, score displays, prompts.

When to avoid: Never. These are always useful.

Patterns: Screen Frame, Character Printing (assembly)

Vault: ULA | ZX Spectrum