Jackpot Payoff

This program implements a slot machine (one-armed bandit) simulation with a graphical display drawn entirely in BASIC using block graphics characters. The machine tracks a running fund starting at $100, deducting $1 per pull and paying out between $2 and $200 depending on the reel combination. Three virtual reels are generated using RND with different range moduli (20, 23, and 23), giving each reel a distinct probability distribution across seven symbol types: asterisk, cherry (O), bar, double-bar, diamond, bell (BAR), and 7. The payout logic uses cascading IF statements to assign a win value W, with W=-1 representing a loss, and a coin-animation sequence simulates the handle pull using FOR/NEXT delay loops. The display features a decorative slot machine cabinet drawn with block graphics, a scrolling dollar-sign payout animation for wins, and the game ends when funds reach zero.

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Program Analysis

Program Structure

The program is divided into clearly separated functional blocks:

1. Lines 1–220: Screen setup — draws the slot machine cabinet and payout table using block graphics, then sets initial loss flag W=-1.
2. Lines 229–310: Switches to SLOW mode, sets starting funds M=100, and jumps to line 1410 to display the initial fund before entering the main loop.
3. Lines 400–440: “INSERT COIN” prompt loop, waiting for the player to press C.
4. Lines 500–580: Coin insertion animation — bounces an “O” character around the screen using short FOR/NEXT delay loops.
5. Lines 600–640: “PULL HANDLE” prompt loop, waiting for P keypress.
6. Lines 700–760: Reel spin animation — prints scrolling bar graphics across the slot window.
7. Lines 800–1050: Reel result generation using RND and cascading IF statements for each of three reels.
8. Lines 1100–1210: Win detection — compares A$, B$, C$ against known winning combinations and assigns payout to W.
9. Lines 1300–1340: Displays the three reel results on screen.
10. Lines 1400–1720: Handles payout display, fund update, win animation, game-over check, and loops back to line 400.
11. Lines 1730–1750: Dead code — CLEAR, SAVE, and RUN are unreachable from normal game flow.

Reel Symbol Generation

Each reel uses a different integer range and a cascade of overwriting IF assignments to map a random number to a symbol string. Because each IF can overwrite a prior assignment, the effective probability of each symbol depends on how many integer values map to it after all comparisons are applied:

Symbol	Reel 1 (R1, 1–20)	Reel 2 (R2, 1–23)	Reel 3 (R3, 1–23)
BAR (%B)	20 only (1/20)	23 only (1/23)	23 only (1/23)
Bar-Bar (\ .\:.)	18–19 (2/20)	20–22 (3/23)	17–18 (2/23)
7	17 only (1/20)	20 only (1/23)	9–16 (8/23)
Asterisk (*)	15–16 (2/20)	15–19 (5/23)	— (0)
Double-bar (\,,)	8–14 (7/20)	9–14 (6/23)	8 only (1/23)
Diamond (\.’)	6–7 (2/20)	6–8 (3/23)	5–7 (3/23)
Cherry (O)	1–5 (5/20)	1–5 (5/23)	1–4 (4/23)

Note that reel 3 has no asterisk symbol, making any asterisk-based win dependent solely on reels 1 and 2, consistent with the payout table which only awards for one or two asterisks.

Payout Logic and Win Flag

The win variable W is initialised to -1 (loss) at line 1100. Each subsequent IF statement can only increase W; there is no guard against multiple matches since the combinations are mutually exclusive by construction. The fund update at line 1405 adds W directly: a loss subtracts 1 (the implied cost of a pull), while a win adds the net prize value minus the implicit $1 cost already deducted.

Key BASIC Idioms and Techniques

• Block graphics in strings: Symbol names like \ .\:., \,, , and \.' are zmakebas escape sequences for block graphic characters embedded directly in string literals and in PRINT statements, giving the display a graphical slot machine appearance without machine code.
• TAB reuse in PRINT: Multiple TAB calls within a single PRINT statement efficiently position both the graphic border and the payout description on the same line (e.g., line 20).
• FOR/NEXT as delay: Empty FOR/NEXT loops (e.g., lines 505–506, 550–551) serve as timing delays for the coin animation. Longer delays use 50 iterations (line 1560).
• FAST/SLOW mode switching: Line 1 uses FAST for rapid screen drawing of the machine cabinet, then line 229 switches to SLOW for normal display during gameplay.
• Cascading IF for symbol selection: Rather than arrays or DATA statements, symbol probabilities are implemented as a chain of IF/LET overrides, a common space-saving technique.
• Win animation: Lines 1500–1610 animate dollar signs cascading down and then restoring the background, simulating coins dropping out of the machine.

Bugs and Anomalies

• FOR loop without NEXT (line 1420): Line 1420 opens a FOR loop (FOR P=1 TO 10) but there is no corresponding NEXT statement. In ZX81 BASIC the interpreter will execute the body of the loop once and then fall through without error if no NEXT is encountered before the end of the program flow reaches a GOTO — effectively making this a no-op delay that never iterates. This is almost certainly a bug where the NEXT was accidentally omitted.
• R1 unused from line 405: Line 405 sets R1=RND before the coin prompt, but R1 is overwritten unconditionally at line 800. This early assignment has no effect on gameplay.
• Reel 3 can produce “£” symbol: Line 995 assigns C$=" £" for R3<23 (22 out of 23 values), but this symbol does not appear in any win-detection condition and is not listed on the payout table. It acts as a guaranteed loss symbol for most of reel 3’s range before being overwritten by subsequent IFs — only values 19–22 (4 values) actually resolve to “£” after all overrides, making it a hidden “near-miss” filler symbol.
• Lines 1730–1750 are unreachable: After line 1720 (GOTO 400), lines 1730–1750 can never execute during normal play; they appear to be leftover development artifacts.