ZXMAN

This program implements a two-dimensional maze-like movement game where the player navigates a character around a grid bounded by asterisk walls. Player position is controlled by keys 5, 6, 7, and 8 (the standard ZX directional keys), and the program tracks a score countdown from a starting value derived from CODE “%£” (the pound sign character code). A randomly appearing ghost character threatens the player, and boundary detection ends the game if the player hits the edges of the play area. All coordinate limits and initial positions are derived from character CODE values rather than literal numbers, saving memory and providing a degree of platform-adaptive positioning.

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Program Analysis

Program Structure

The program is organised into four logical phases:

1. Initialisation (lines 10–50): All key constants are derived from CODE of specific characters rather than hard-coded literals.
2. Screen draw (lines 60–100): A bordered play field of asterisks is printed, with a title banner.
3. Game loop (lines 110–200): A FOR loop counts down the score; inside it, player input is read, the player sprite is moved, boundary and goal checks are made, and a ghost is randomly placed.
4. End states (lines 210–250): “TIMES UP”, STOP, CLEAR, SAVE, and RUN provide restart infrastructure.

Character-Code Constants

Rather than embedding raw numbers, the program derives all key values from CODE of printable characters. This is a common memory-saving idiom on Sinclair machines where short expressions can replace longer literal strings in tokenised BASIC.

Variable	Expression	Resolved value	Role
L	CODE " "	32	Space character code; used as a general-purpose constant (column 32, loop start, edge detection)
A, B, M	CODE "▘" (block graphic char)	130	Initial player row/column and step size — but see anomaly note below
I	CODE "("	40	Right boundary column
Loop end/ghost range	CODE "%£" (inverse £)	96	Score countdown start and ghost random range
Loop bound line 70	CODE "\~~"	Approximately 14	Number of rows to draw wall lines
Bottom edge	CODE ":"	58	Lower boundary row for kill detection

Note: A and B are initialised to CODE "▘" (130) which far exceeds the ZX81’s screen coordinate space (rows 0–21, columns 0–31). This means the player sprite is placed off-screen at the start, which is a likely bug — the player’s initial position should probably be a small on-screen coordinate.

Key Input and Movement

Movement uses the standard five-key layout. Lines 120–130 update player coordinates:

• INKEY$="6" increments row A (down)
• INKEY$="7" decrements row A (up)
• INKEY$="8" increments column B (right)
• INKEY$="5" decrements column B (left)

The player sprite ("C") is printed at position AT A,B and then erased with a space on the next iteration (line 160), implementing basic sprite flicker movement without any machine code.

Game Mechanics

The score countdown runs via FOR F=CODE "%£" TO L STEP -M (line 110), decrementing from 96 toward 32 with a step of -M (which equals 130, making the step far larger than the range — the loop will execute only once or not at all as intended). This is another consequence of the off-screen initial value of M.

Boundary detection (line 170) kills the player if A=L (row 32), A=CODE ":" (row 58), B=L (column 32), or B=I (column 40). These bounds seem plausible for a sub-region of the display but depend on the player actually reaching on-screen coordinates.

The ghost (line 190–199) is placed when E=A and B<A, where E is a random integer in 0..95. The condition B<A acts as a proximity guard.

A goal condition on line 155 checks A=M AND B=I-M, printing a score if the player reaches a target cell.

Notable Techniques and Anomalies

• The use of W (which is never initialised) in PRINT statements at lines 155, 170, and 190 will print a default value of 0, but suggests W was intended as a lives counter that was never fully implemented.
• Lines 230–250 (CLEAR, SAVE, RUN) are unreachable during normal execution due to STOP at line 220, but provide a manual-reset / save block that can be reached by editing the flow.
• The score display label "ZX LIVES" and kill message "ZX KILLED" appear to be formatting strings where ZX is used as a separator or newline substitute — on ZX81 BASIC, these would print as literal text without special meaning.
• The play field is drawn using inverse-video block graphic characters mixed with asterisks, creating a bordered arena purely through PRINT statements with TAB positioning.