Bowling Alley

This program simulates a simplified ten-pin bowling alley game in BASIC. It tracks ten frames, two balls per frame, and uses a 10-element array A() to represent the ten pins. Pins are set by storing character code 52 (the digit “4”, used as a standing-pin marker) and knocked down by switching to code 23 when a random number exceeds 0.5. The triangular pin layout is rendered using CHR$ codes and TAB positioning across four PRINT lines, giving a visual triangle arrangement. A running high score Y persists across games by looping back to line 30 rather than restarting the program, and a strike on the first ball is detected at line 220, jumping to a special handler that awards a bonus.

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Program Analysis

Program Structure

The program is organized into a main game loop (lines 20–290), a post-game summary (lines 300–350), and a strike handler subroutine (lines 370–400). The outer FOR B=1 TO 10 loop iterates over frames, and the inner FOR E=1 TO 2 loop covers the two balls per frame. High score tracking persists by looping to line 30 (which resets only the frame score S) rather than rerunning the program, so Y accumulates across games.

Pin Representation

The ten pins are stored in array A(10). A standing pin is represented by character code 52 (the ASCII/BASIC character 4), and a knocked-down pin is represented by code 23 (a graphic block character). On the first ball (E=1), all pins are reset to 52 at line 110. On the second ball, line 100 skips the reset so remaining pins keep their knocked-down state. Each pin is randomly knocked down at line 120 if RND>0.5, giving roughly a 50% per-pin probability.

Pin Layout Display

Lines 150–180 render the classic triangular pin layout using TAB and CHR$ A(n). The pins are arranged as:

• Row 1 (back): pins 10, 9, 8, 7 — TAB 8
• Row 2: pins 6, 5, 4 — TAB 9
• Row 3: pins 3, 2 — TAB 10
• Row 4 (front): pin 1 — TAB 11

This produces a visually correct inverted triangle. The characters displayed are either 4 (standing) or the code-23 block graphic (fallen).

Scoring Logic

The knocked-down count Z is accumulated in the loop at lines 90–140 by counting pins with code 23. On the second ball, S is incremented by 1 at line 240 regardless of how many pins were knocked down — this is a notable simplification rather than true ten-pin scoring. A strike (all 10 pins on ball 1, detected at line 220) jumps to the strike handler, which sets S=3+15=18 at line 390, a hard-coded bonus. Line 230 then caps Z at 15 if it exceeds 9, though this is used more to signal “full rack” than as a standard spare/strike score.

Ball Label Using CHR$

Line 60 prints CHR$ (E+156) for the ball label. When E=1, this gives CHR$ 157 and when E=2, CHR$ 158 — these are UDG characters \n and \o on the TS2068, so the ball number is displayed as a UDG rather than a plain digit, likely unintentionally producing graphic characters unless those UDGs happen to be defined.

Input Handling

Line 260 polls INKEY$ in a tight loop waiting for CHR$ 118, which is the NEWLINE/ENTER key, before advancing to the next ball. This is a standard busy-wait keypress idiom in Sinclair BASIC.

Bugs and Anomalies

• The scoring at line 240 increments S by only 1 per frame completion, ignoring the actual number of pins knocked down. True bowling scoring is not implemented.
• The strike handler at line 390 uses LET S=3+15 (evaluating to 18), which overwrites the current total score rather than adding a bonus to it — a significant scoring bug.
• After a strike, E is set to 2 at line 380 and execution falls into line 230, but the FOR E loop state is now inconsistent; the NEXT E at line 280 will still try to execute, potentially causing issues depending on interpreter behaviour.
• Line numbers 200 and 210 are absent (jumped over), suggesting deleted or renumbered lines.
• The CHR$ (E+156) ball label produces UDG characters rather than the digits 1 and 2, which appears unintentional.