Muncher II

Muncher II is a Pac-Man–style maze game written in BASIC by James S. Broaddus (1983) in which the player navigates a character through a 21×21 grid collecting dots, power pellets, and bonus items while evading two ghosts. The entire maze is stored as a two-dimensional string array B$(21,21), with each cell representing a wall (“% “), dot (“.”), power pellet (“*”), tunnel (“-“), or space, allowing collision detection by simple string indexing. Two ghosts are tracked by separate coordinate pairs (GX/GY and GX1/GY1) and move by comparing their position to the player’s coordinates, with a skill-level parameter A controlling how often random direction changes override pursuit. Eating a power pellet (line 2000) sets a counter C to −1 and a COUNT timer so that ghosts temporarily display in a vulnerable appearance and are worth bonus points if caught. The tunnel mechanic at the left and right walls is implemented by checking for the “-” character and wrapping the player’s X coordinate between columns 2 and 20.

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Program Analysis

Program Structure

The program is organised into several distinct functional blocks reached by GOTO and GOSUB:

• Lines 1–7: Variable initialisation and skill-level selection subroutine (GOSUB 7000).
• Lines 8–210: Maze construction — each row of the 21×21 board is assigned to B$(N) as a literal string.
• Lines 220–240: Initial maze render loop.
• Lines 250–600: Main game loop covering player input, movement, scoring, ghost AI, and win/loss detection.
• Lines 1000–1040: Bonus item (“£”) spawning subroutine.
• Lines 1500–1650: Horizontal movement handlers with tunnel-wrap logic.
• Lines 1700–1830: Vertical movement handlers.
• Lines 2000–2060: Power-pellet consumption — activates vulnerable ghost mode.
• Lines 3000–3110: Ghost movement execution — each branch moves a ghost coordinate then jumps into the continuation of the ghost-update block.
• Lines 4000–4020: Stop-movement handler for unrecognised keys.
• Lines 5000–5080: Level-clear animation (sweeping line across row 10) and restart.
• Lines 7000–7110: Title screen and skill-level input.
• Lines 8000–8110: Ghost-catch scoring — awards points and resets ghost positions.
• Lines 9000–9600: Death/game-over sequence, high-score update, and SAVE.

Maze Representation

The maze is held in a DIM B$(21,21) two-dimensional string array where each element is a two-character cell. Wall cells contain "% " (percent-space), dots are "." plus a space, power pellets are "*", tunnel exits are "-", and the bonus item is represented by "£". Because BASIC’s DIM pads shorter strings, assigning a 42-character string to a 21-element row fills every two-character cell simultaneously. Collision detection is then performed by reading individual cells such as B$(Y,X+1) directly.

A practical consequence is that the program never builds a separate collision map — the display state is the game state. Eating a dot or pellet is effected by LET B$(Y,X)=" " at line 400, which simultaneously clears the map and prevents re-collection.

Player Movement

Direction is encoded in two variables: R (horizontal delta, −1/0/1) and E (vertical delta, −1/0/1). Movement keys 5/6/7/8 route to subroutines at lines 1500–1830 that update R, E, and the avatar character A$ (">", "<", "A", "V"). Any other non-directional key jumps to line 4000 which zeroes both deltas, halting the player. The actual position update at lines 370–371 tests the destination cell before committing the move.

Tunnel Mechanic

Row 12 of the maze contains "-" characters at columns 1 and 21, representing tunnel exits. The movement routines detect a "-" in the direction of travel and set CHECK=0, which causes lines 1530/1630 to teleport X to column 2 or 20 respectively before continuing normal movement processing.

Ghost AI

Two ghosts share coordinate pairs (GX,GY) and (GX1,GY1). Each game-loop iteration compares the ghost coordinates to the player’s Y,X and attempts to step toward them if the destination cell is not a wall. The skill-level parameter A (range 0.2–0.6, lower = harder) is used as a probability threshold: IF RND<A THEN GOTO [skip] at lines 425, 436, 446, 456, 465, 474, 478, 486 randomly bypasses each pursuit decision. Lower A values skip fewer steps, making ghosts pursue more reliably.

Power-Pellet and Vulnerable Mode

Eating a "*" cell (line 375 → subroutine 2000) sets movement-step variable C to -1 and resets COUNT to 0. C normally equals 1; when −1, ghost movement subroutines step coordinates in the opposite direction (effectively reversing pursuit). Ghost appearance changes: lines 520–535 print "%"" (inverse ghost) when C=1 and plain """" when C=-1. Lines 500–510 increment COUNT and restore C=1 when it reaches 30, ending vulnerable mode.

Scoring and Win Condition

Item	Points	T adjustment
Dot (".")	+1	—
Power pellet ("*")	+10	+10 (adds to target)
Bonus item ("£")	+10	+10
Catch ghost (vulnerable)	+10	+10

The win condition is S=T (line 415). T is initialised to 180 and incremented when power pellets and bonus items are added to the board, keeping it synchronised with total collectable points. On level clear, line 5070 adds 180 to T before looping to line 8 to reset the maze without resetting the score.

Bonus Item Spawning

Line 330 calls GOSUB 1000 with probability 1/50 per loop iteration. The subroutine places a "£" at the fixed position (row 14, column 11) only if that cell is empty. If a dot was previously there, line 1020 decrements T by 1 (since the dot was already counted in T) and the "£" replaces it at higher value, preserving score balance.

Death and Game-Over Sequence

A ghost catching the player (lines 540/550) routes to line 9000. If COUNT<=30 the player is in a power-up window and the ghost is caught instead (subroutine 8000 awards points and respawns the ghost). Otherwise, a life is lost. The death animation at lines 9010–9019 alternates printing A$ and CHR$(CODE A$+128) (the inverse-video version of the avatar character) in a short loop. At zero lives, the high score is updated and a restart prompt is shown.

Notable Techniques and Anomalies

• The SAVE "1025%2" at line 9590 uses an inverse-video “2” in the filename — on Sinclair BASIC this is the auto-run flag embedded in the filename, causing the program to RUN automatically when loaded.
• Line 1810 contains a copy-paste bug: the down-movement guard checks B$(Y-1,X)<>"-" instead of B$(Y+1,X)<>"-", making the downward-movement tunnel guard test the wrong row.
• Lines 3060 and 3070 incorrectly write LET GY=GY1+C (overwriting ghost 1’s Y with ghost 2’s Y plus C) instead of LET GY1=GY1+C. This is a variable-name bug causing ghost 1 to be displaced when ghost 2 moves right.
• The level-clear animation at lines 5010–5060 prints a sweeping pattern across row 10, using embedded ">" and "<" characters to simulate a wiper effect before restarting at line 8.
• A$ doubles as both the display character and a state indicator for direction — direction-sensitive scoring or behaviour could easily be added by testing A$.
• Line 8060 contains a logic error: IF GY>=X OR GX1<>Y should likely be GY1>=X to compare ghost 2’s column against the player, mirroring the ghost-1 check at line 8000.