Yachtzee

This program implements the dice game Yahtzee for one to four players on a 15-row scorecard. Each player takes up to three throws per turn, choosing which of the five dice (labelled A–E) to re-roll by entering a string of letter choices. The scorecard layout is encoded in the single long string Z$ at line 110, sliced into 10-character fields for display. Scores are stored in a two-dimensional array P(PLYRS,15), where column 15 holds each player’s running total and columns 7–8 track the upper-section subtotal and bonus.

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Program Analysis

Program Structure

The code is divided into clearly separated routines accessed via GOSUB:

1. Lines 10–110 – Global constants and data: player-name string T$, layout string Z$, display offsets P1, LE, P2, P3, bonus threshold PLUS.
2. Lines 800–990 – Setup: player-count input, array initialisation, scorecard draw (GOSUB 8000).
3. Lines 1000–2340 – Main game loop: throw loop (up to 3), option selection, scoring dispatch.
4. Lines 3000–3160 – Score recording, player cycling, end-of-game winner display with a flashing loop.
5. Lines 7010–7100 – Winner determination subroutine.
6. Lines 8010–8120 – Screen draw subroutine (scorecard labels + player headers).
7. Lines 9010–9110 – Dice-roll subroutine; only dice whose letter appears in A$ are re-rolled.
8. Lines 9210–9260 – Count-array builder (DIM C(6), tally of each face value).
9. Lines 9310–9940 – Individual scoring subroutines: Yacht (5-of-a-kind, 50pts), 4-of-a-kind, Full House / High Straight, Big Straight, Little Straight, Choice (sum all), upper-section numbers.
10. Lines 9950–9970 – CLEAR / SAVE / RUN auto-restart block.

Scorecard Layout Encoding

The string Z$ at line 110 is exactly 150 characters long (15 rows × 10 characters each). The subroutine at line 8010 slices it with Z$(PS TO PF) using computed offsets and prints each slice at the corresponding screen row, providing the entire left-hand label column of the scorecard without any individual PRINT statements per row. The constant LE=10 controls field width.

Display Coordinate System

Column positions for each player’s scores are computed from three constants:

• P1=1 – base left margin
• P2=5 – per-player column stride
• P3=12 – right offset from left margin to score columns

The expression (PL-1)*P2+P1+P3 therefore yields column 13 for player 1, 18 for player 2, etc., giving a compact multi-column scorecard for up to four players.

Score Array Layout

Index	Contents
1–6	Upper section (ones through sixes); initialised to -1 (unscored)
7	Upper subtotal (accumulates as entries are made)
8	Bonus flag (0 = not awarded, 50 = awarded)
9–14	Lower section categories (Choice, Full/High Straight, 4-of-a-kind, Little Straight, Big Straight, Yacht)
15	Grand total (running sum)

Unscored cells are initialised to -1 so that a score of 0 (a valid outcome) is distinguishable from an empty slot. The guard at line 2060 (IF P(PL,OP)>=0 THEN GOTO 2010) prevents overwriting an already-scored category.

Option Numbering Offset

The user enters options 1–12. Because the score array reserves slots 7 and 8 for the subtotal and bonus (not directly selectable), line 2052 adjusts: IF OP>6 THEN LET OP=OP+2. This maps user choices 7–12 to array indices 9–14, skipping the internal slots cleanly.

Dice Re-roll Mechanic

Dice are labelled A–E via T$="ABCDE". The player types a string of letters for dice to keep (or re-roll — the logic at lines 9010–9070 re-rolls any die whose letter appears in A$). On the first throw, A$ is pre-set to "ABCDE" at line 1006 so all five dice are always rolled. Subsequent throws prompt the player to enter letters.

Scoring Subroutines

All scoring routines rely on the count array C(6) built by the subroutine at line 9210. The count array is declared with DIM C(6) inside the subroutine, which resets it to zero on each call — a neat initialisation trick. Key scoring logic:

• Yacht (line 9310): checks for any C(N)=5; awards 50 points.
• 4-of-a-kind (line 9410): checks C(N)>=4, then sums all dice.
• Little Straight (line 9510): calls GOSUB 9800 to count zero-valued slots (CT); awards sum of dice if exactly 4 distinct values present (CT=4 gaps in C means… see anomaly below).
• Full House / High Straight (line 9610): awards 30 if C(6)=0 and CT=1 (one face missing, no sixes — i.e. 1–5 straight or full house heuristic).
• Big Straight (line 9710): awards 30 if C(1)=0 and CT=1 (2–6 straight).

Notable Techniques

• FAST / SLOW (lines 900, 990) bracket the array initialisation and screen setup for speed.
• The winner-display loop (lines 3090–3160) uses two short FOR…NEXT delay loops and alternates the winner name with a blank to create a flashing effect without PAUSE.
• RAND at line 832 seeds the random number generator from the real-time clock, ensuring different dice sequences each game.
• The SAVE "1025%4" at line 9960 uses an inverse-video character in the filename as an auto-run flag.

Bugs and Anomalies

• Missing GOSUB 7000: Line 3080 calls GOSUB 7000 but the subroutine begins at line 7010. This is a standard technique of jumping past the first line of a subroutine via a non-existent entry point — here it works because there is no executable code at line 7000 itself and execution falls through to 7010.
• Little Straight scoring: The subroutine at 9510 checks CT=4 (four empty slots in C), which would mean only two distinct values are present — the opposite of a straight. A genuine 1–2–3–4 straight would have CT=2. This appears to be a logic error; the intended check was likely CT=2.
• Full House / High Straight conflation: Option 8 is labelled “FULL/HS” (Full House / High Straight) but the scoring subroutine only checks for a 1–5 straight (no sixes, one missing value). A genuine full house (e.g. three 2s and two 5s) would also give CT=2, not CT=1, and would not be caught.
• Grand total double-counting: The upper-section bonus (50 pts) is added to P(PL,15) at line 2150, and each scored option also adds to P(PL,15) at line 3012. However, the upper subtotal (slot 7) is also added at line 3012 when the player nominates an upper-section option, meaning the upper-section points are counted twice in the grand total (once via slot 7 and once via slots 1–6).
• A$ as keep-or-reroll ambiguity: Lines 1006 and 9040–9050 re-roll dice whose letters appear in A$, but the prompt at line 1010 says “CHOOSE” with no indication of whether the player should enter dice to keep or dice to re-roll.