Super Slot-O

This program simulates a one-armed bandit (slot machine) game called “Super Slot-O.” Each spin generates three random characters drawn from one of two pools: printable ASCII characters (codes 2–7, block graphics) or Spectrum-style graphic characters (codes 128–132), selected by a 50/50 RND branch at line 500. The three results are compared pairwise using flags P, Q, and R to detect matching pairs, and the combination of those flags determines whether the player wins $5 (two of a kind), $10 (three of a kind), or nothing. The game loops indefinitely with no bankroll tracking, initialising all flags via a GOSUB 900 subroutine before each spin.

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Program Analysis

Program Structure

The program is organised into a main loop and several subroutines:

• Lines 10–90: Title display, instruction prompt (GOSUB 800), variable initialisation (GOSUB 900), and wait for a keypress.
• Lines 100–390: Main game logic — three spins via GOSUB 500, pairwise comparison, result display, then loop back to line 20.
• Lines 500–720: Random character generation subroutine with two branches.
• Lines 800–820: Instruction text subroutine.
• Lines 900–960: Variable reset subroutine.

Character Generation Algorithm

The subroutine at line 500 uses a binary RND branch to choose between two character pools:

Branch	Lines	Character range	Description
Lower (RND < 0.5)	600–620	CHR$ 2 – CHR$ 7	Low block/graphic characters
Upper (RND ≥ 0.5)	700–720	CHR$ 128 – CHR$ 132	UDG / block graphic characters

The lower branch loops until INT(8*RND) yields a value ≥ 2 (giving codes 2–7). The upper branch loops until INT(133*RND) yields a value ≥ 128 (giving codes 128–132). Both branches use rejection sampling to avoid unwanted character codes.

Win Condition Logic

Three Boolean flags P, Q, and R record pairwise matches: P for A=B, Q for B=C, R for C=A. Their sum is then used to classify the result:

• P+Q+R = 1 → exactly one pair matches → “Two of a Kind” → $5
• P+Q+R > 1 → two or three pairs match (i.e. all three equal) → “Three of a Kind” → $10
• P+Q+R < 1 → no matches → no win

Note that if all three values are equal, all three flags are set and their sum is 3, correctly triggering the three-of-a-kind branch. Two of a kind (exactly two symbols the same) sets exactly one or two flags depending on which pair matches; however since the three comparisons are not mutually exclusive, two matching symbols always set exactly one flag, making the logic sound in practice.

Variable Initialisation

The subroutine at lines 900–960 resets all six flags (P, Q, R, S, T, U) to zero before each spin. It is called once at startup (line 70) but the main loop at line 390 returns to line 20, skipping the GOSUB 900 call. This means the flags are not reset between rounds, which is a bug: a win on one round can carry its flag state into the next, causing incorrect win announcements.

Key BASIC Idioms

• Using IF INKEY$="" THEN GOTO 90 (line 90) as a busy-wait keypress loop.
• Using IF flag THEN ... directly as a Boolean test (lines 320–370), relying on non-zero being truthy.
• PAUSE 60 (line 310) inserts a one-second delay before displaying results.
• RAND at line 6 seeds the random number generator for variety between runs.

Bugs and Anomalies

• Missing flag reset in main loop: GOSUB 900 is only called once before the first game. From line 390 the program jumps back to line 20, bypassing the reset. All six flags retain their previous values, corrupting subsequent win detection.
• No bankroll tracking: Dollar amounts are printed but never accumulated or deducted; there is no concept of a starting stake or game-over condition.
• Cosmetic loop: The star banner (lines 20–50) reprints on every loop iteration including mid-game redraws, which may cause screen clutter since CLS at line 100 only runs once after the initial keypress.