Treasure Hunt

Treasure Hunt is a real-time dungeon exploration game in which the player navigates a network of interconnected caves searching for gold, avoiding rock walls and pursuing demons. The cave map is encoded compactly in string B$ at lines 70–76, where each room’s three exits are stored as ASCII characters offset by 37, allowing up to 21 rooms including a special Treasure Room (room 21). Movement uses the classic Sinclair 5/6/7/8 key layout, and the player can fire arrows in a chosen direction by pressing F followed by a direction key. The program uses PEEK of the display file base address (obtained at line 55 via PEEK 16396/16397) to detect collisions with cave walls and other obstacles without maintaining a separate map array. A score/economy system lets the player bank treasure between runs, buy extra arrows at 4 points each, and survive death with a 15-point penalty if their cumulative score is high enough.

---

Program Analysis

Program Structure

The program is divided into several functional regions:

1. Lines 1–95: Initialisation — arrays, string constants, score variables, display-file address, map data, and random seed.
2. Lines 150–360: Cave rendering and main game loop — draw walls, place demons, move hero, handle arrow firing, and detect collisions.
3. Lines 605–970: Room-switch logic — tunnel display, exit lookup from B$, and re-entry into the drawing routine.
4. Lines 1000–1125: Arrow-firing subroutine.
5. Lines 1200–1255: Demon movement subroutine.
6. Lines 1295–1660: Start sequence, entrance hall, treasure banking, and arrow purchasing.
7. Lines 2000–2040: Death handler with conditional continue.
8. Lines 2045–2115: Treasure Room setup (room 21).
9. Lines 2999–3035: Trap/guardian movement subroutine used only in the Treasure Room.

Cave Map Encoding

The 21-room graph is stored in string B$ (lines 70–76) as a flat sequence of ASCII characters. Each room occupies three consecutive characters representing its three exits. Exit numbers are recovered by subtracting 37 from the character code, so the digit 9 (ASCII 57) maps to room 20, A (65) to room 28, etc. The decoding occurs at lines 920–945:

• R1 — left/top exit (displayed at top of screen)
• R2 — right/bottom exit (displayed at bottom)
• R3 — third exit used as a replacement when the player came from R1 or R2

Lines 960–965 swap out the “back” exit so the on-screen numbers always show two new destinations, preventing the player from trivially retracing steps.

Display-File Collision Detection

Line 55 calculates Q, the base address of the display file, using the system variables at addresses 16396–16397. During gameplay, PEEK (Q+33*N+M) reads the character code at the hero’s target cell; any value above 62 (i.e., not a space or normal ASCII) triggers death (line 325), and code 23 (the * treasure marker) awards 10 points (line 330). Code 8 is treated as a wall/obstacle that simply blocks movement (line 335). This technique avoids maintaining a separate collision map entirely.

Random Cave Generation

Each cave room is procedurally drawn at lines 165–210. RAND (PR*10+NOW) seeds the generator with a combination of the room number and a session seed (NOW, set once at line 68), so the same room always looks identical within a session but differs between sessions. Block graphics characters (codes 128–130 and the \:. graphic) and random positioning create stalagmite/stalactite shapes.

Demon AI

Up to three demons are tracked in the 2D array D(3,2). Each demon moves one step per call to the subroutine at line 1200 using SGN(N-Y) and SGN(M-X) — a simple but effective Manhattan-direction chase. If a demon reaches the hero’s cell (M,N), execution jumps to the death routine at 2000. The demon count DEM can spontaneously increase from 0 to 1 during movement (line 340, probability 3%), and the arrow-firing routine decrements DEM and shuffles the array to remove a hit demon (lines 1100–1110).

Arrow Firing

The subroutine at lines 1000–1125 waits for a direction key after F is pressed. The arrow travels one cell at a time, printing + then erasing it, until it hits a non-zero display cell or goes off-screen. On hitting a demon’s cell it prints an inverse + (%+), awards 5 points to S, and removes the demon. In the Treasure Room the final arrow position is also stored in FX/FY for use by the guardian subroutine.

Treasure Room (Room 21)

Room 21 is a special diamond-shaped chamber drawn by the loop at lines 2055–2080 using string slicing of C$. A guardian creature is set up with variables J, K, MY, MX and updated each frame via GOSUB 3000. The guardian bounces between directions when it would walk into a non-zero cell (lines 3002–3008), creating simple wall-reflection behaviour. The treasure itself is represented by clusters of *** at randomised positions.

Economy and Death System

The player carries two score accumulators: TR (treasure collected in the current run, lost on death unless the score threshold is met) and S (banked score). Returning to the entrance safely banks TR into S (line 1540). On death, if S+TR < 50+PS the game stops outright; otherwise 15 points are deducted and play resumes from the entrance (lines 2020–2040). The variable PS records the previous best combined score to raise the continuation threshold progressively.

Notable Techniques and Anomalies

• Boolean arithmetic for movement: Lines 310–315 use (1 AND INKEY$="8") etc. to compute directional deltas without IF statements — a common Sinclair BASIC idiom.
• String-encoded map: Packing the entire cave graph into a single string literal is an efficient alternative to a numeric array.
• Line 3000 potential bug: PEEK (Q+33*(K+MY)+K+MX) should likely be Q+33*(K+MY)+(J+MX) — the guardian’s X-coordinate J is missing; K is used twice, so the wall-bounce check reads the wrong screen cell. The guardian still moves but direction reversal is unreliable.
• Line 822 dead-end: If both R1 and R2 happen to equal LR (the last room), PR could be set to 0, causing the branch at line 822 to jump to line 1505 (the safe-house message) instead of a valid room.
• C$ construction: The decorative border string is built in three concatenated assignments (lines 11, 13, 15) to stay within the line-length limit, then sliced with C$( TO AI) in the Treasure Room loop for the diamond-border effect.

Key Variable Summary

Variable	Role
PR	Current room number (1–20, or 21 = Treasure Room)
LR	Last room visited (used to exclude back-exit)
N, M	Hero row and column
DEM	Number of active demons (0–3)
D(I,1/2)	Demon row/column coordinates
TR	Unbanked treasure score for current run
S	Banked score
ARR	Arrows remaining
Q	Display file base address
B$	Packed cave exit map
T(I)	Treasure-present flag for each room
J, K	Treasure Room guardian column/row
FX, FY	Last arrow impact position (Treasure Room)