Crash

This program implements a three-lane ball-catching game in Sinclair BASIC. The player controls a moving catch zone using the Z and M keys to deflect a falling ball, which travels downward across the screen in a FOR loop from row 40 to row 2. Three targets (lanes at pixel columns 6, 26, and 46) each have a hit counter represented by a string of block-graphic characters; a successful deflection triggers a second upward ball trajectory, and scoring occurs when that ball lands at column 30. Lives are tracked in variable T (starting at 2, incremented at each round start), and the display uses inverse-video characters for the score header and lane markers. The SAVE command at line 1070 uses an inverse digit in the filename as an auto-run flag.

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Program Analysis

Program Structure

The program flows through a main game loop anchored at line 125 (CLS and redraw), with two inner FOR loops handling ball movement. Lines 10–120 perform initialisation, and line 30 is the round-start target where lives (T) are incremented each time all three lanes are cleared. The end-of-game sequence begins at line 325, with a replay prompt at line 1000.

Game Mechanics

A ball falls from pixel row 40 to row 2 (line 170–210), plotted one pixel per iteration. The player steers its horizontal position E using Z (decrement) and M (increment) via INKEY$. If the ball lands at column 6, 26, or 46, the corresponding lane counter (B, C, or D) is decremented, and a second ball travels upward from row 2 to row 40 (lines 263–295), steered by variable G. A score point is awarded only if this return ball reaches column 30 exactly (line 300).

Display Layout

The screen uses a mixture of PRINT AT, TAB, and string slicing to render lane indicators. The lane hit-counters are displayed as substrings of B$, C$, D$ sliced to lengths B, C, D respectively (line 150), each initialised to "% % % % " (eight characters of alternating inverse-space and space). As a lane is hit, its substring shortens visually. The header line (line 135) prints the lives counter T and score X, with an inverse-video block-graphic separator.

Variable Reference

Variable	Purpose
T	Lives remaining (starts at 2, incremented each new round at line 30)
X	Player score
B, C, D	Hit counters for the three lanes (initially 4 each)
E	Horizontal position of the falling ball
G	Horizontal position of the return ball
F$	Block-graphic string used for lane markers ("\. ")
B$, C$, D$	Lane indicator strings, sliced to length of remaining hits
Z, Y	FOR loop counters for ball row positions
P	Delay loop counter at crash display
Q$	Replay prompt keypress

Key BASIC Idioms

• String slicing with ( TO B) etc. (line 150) shortens the displayed lane marker as hits accumulate — a compact visual depletion bar.
• INT (RND*50)+1 is used at lines 165 and 263 to randomise the starting horizontal position of each ball.
• A short FOR/NEXT loop (P=1 TO 50, lines 343–344) provides a crude delay after “CRASH” is displayed.
• Lines 325–327 clamp lane counters from -1 back to 0 to prevent string-slice errors on the next redraw.

Notable Techniques and Anomalies

The lives variable T is initialised to 2 at line 10 but is incremented at line 30 before any display, so the player effectively starts with 3 lives. Each crash decrements T at line 341; when T reaches 0 the game ends. The condition at line 130 checks T>0, meaning once all lives are consumed the loop to line 30 is skipped and play falls through to the crash/end sequence on the next iteration.

The ball’s horizontal position is never bounds-checked, so holding Z or M for extended periods during the fall loop can push E or G outside the valid pixel range (0–255), which would cause a BASIC error on the PLOT statement. There is also no check that the return ball’s column G stays within screen bounds.

Line 1060 (CLEAR) and lines 1070–1080 are unreachable during normal play, as line 1050 (RUN) restarts the program before they are reached. They appear to be development/save remnants left in the listing.