3 Games

This program bundles three separate games—Minefield, a simple Pong clone, and a Night Driver–style 3D driving game—into a single BASIC listing with a menu system starting at line 1500. Minefield moves up to three player tokens along a track divided into multiples of four, where landing on such positions triggers a “mine” flag stored in a two-dimensional array. The Pong game uses a single-character ball and a paddle controlled by keys 5 and 8, with BEEP calls for audio feedback on wall bounces and paddle hits. The Night Driver segment defines a custom four-character UDG car sprite via POKEd DATA bytes and draws converging road lines using PLOT/DRAW, adjusting a horizontal position variable to simulate steering and detecting crashes when the position drifts outside bounds.

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Program Structure

The listing is organized into four distinct regions, each entered via RUN with an explicit line number rather than GO TO, which restarts the interpreter and clears variables each time:

Lines	Section
10–330	Minefield game
500–690	Pong game
1000–1340	Night Driver game
1500–1560	Main menu / dispatcher

Line 5 (RUN 1500) ensures the menu is shown on program load. The menu at line 1530 validates input in-line with IF (a<1) OR (a>3) THEN RUN, which re-runs from the top of the program (line 5), looping back to the menu.

Minefield — Key Mechanics

State for the three player tokens is kept in array a(PI,2), which on the Spectrum evaluates PI as 3, giving a 3×2 array. Column 1 (indexed via SGN PI = 1) holds each man’s current position; column 2 holds a dead flag.

• A random dice roll x (1–6) is generated each turn.
• Mine detection at line 150: a position is mined if it is an exact multiple of 4 (p = INT p where p = pn/4) or equals 25 specifically. Landing there sets a(m,2)=1 (dead).
• The finish square is column 28; reaching it increments the win counter w.
• Win/loss checks at lines 220–250 cover all-dead, all-arrived, and the mixed game-over case.
• Invalid moves (selecting a dead or already-finished man) jump to line 280 and display an error for a short busy-loop delay before clearing it.
• The idiom IF INKEY$=i$ THEN GO TO 260 at line 260 debounces the key held from the previous input.

A notable anomaly: DIM c$(32) is declared but used only at line 290 as a 32-space string to blank the “INVALID MOVE” message — a clean erase technique.

Pong — Key Mechanics

The ball is a single "." character. Position is tracked by x (row) and y (column); direction by ud (±1 vertical) and lr (±1 horizontal). The paddle is at fixed row A=20, column b, drawn as CHR$ 95 (underscore).

• The subroutine at lines 660–690 reads keys 8 (right) and 5 (left) and redraws the paddle each frame — called twice per loop iteration (before and after moving the ball) for smoother response.
• Wall bounces at ny=0 or ny=31 reverse lr and set flag w=10 (used to trigger a BEEP on the next frame via IF w THEN BEEP .01,30).
• A miss (ball reaches row 22) plays a low BEEP and restarts the ball via GO TO 550, preserving the paddle position.

Line 510 contains a developer note embedded in a REM: REM LINE 50, value of w unknown:LET w=?. This references the Minefield section’s variable w and flags that because each game is entered with RUN, variables are reset, but the comment appears to document a concern that was ultimately moot.

Night Driver — UDGs and Graphics

The car sprite is four UDG characters (a–d), arranged in a 2×2 block, defined by POKEing 32 bytes of DATA into USR "a" through USR "d"+7 via the subroutine at lines 1270–1290.

Road perspective is simulated with two pairs of PLOT/DRAW calls that draw converging lines from the bottom of the screen toward a vanishing region, using the horizontal position variable p (nominally centered at 127):

• PLOT p-10,159: DRAW -170+(p-10),-159 — left road edge
• PLOT p+10,159: DRAW -70+(p-10),-159 — right road edge (asymmetric offset creates a subtle skew)

Each game tick erases the previous lines using PLOT OVER 1 / DRAW OVER 1 (XOR mode), then redraws at the new p. The crash condition checks whether p has drifted outside the range 108–150 (line 1040). When a crash occurs, lines 1140–1150 draw the final road position without erasing, then play an ascending BEEP sweep at line 1170.

The score sc increments by 1 each loop iteration (line 1110), giving a simple survival-time score. Steering input moves p by ±4 pixels per key press, and a random drift of ±10 pixels is added each frame (INT(RND*20)-10), making the road progressively harder to follow.

Notable Techniques and Idioms

• SGN PI is used throughout as a constant 1, avoiding the literal digit to save a byte per occurrence.
• NOT PI evaluates to 0, used as a column argument in PRINT AT statements for left-aligned output.
• VAL i$ converts the single-character key input to a numeric man-selector without an explicit variable assignment step.
• RUN 10, RUN 500, RUN 1000 as game launchers cleanly reset all variables without needing explicit initialization in each game section (except for the Night Driver which uses its own GO SUB 1220 init routine).
• The INPUT "" LINE a$ at line 1190 waits for ENTER without displaying a prompt variable — the prompt text is embedded directly in the INPUT string.

Bugs and Anomalies

• In Pong, the bounce flag w is set to 10 on a side-wall hit but only 1 on a top-wall hit (line 590). Since the BEEP check at line 560 is IF w (any nonzero), both trigger a beep — the value 10 has no additional effect, suggesting a copy or edit artifact.
• The Night Driver road line geometry is asymmetric: the right-edge DRAW uses -70+(p-10) rather than the expected mirror of the left edge’s -170+(p-10). This means the right road line converges less steeply, producing a slightly off-center vanishing point.
• Line 1200 (GO TO 1040) is unreachable dead code, sitting after the INPUT / RUN sequence in the crash handler.
• The menu’s instruction at line 1520 prints " 2 & 3 use 5 for right" — but key 5 moves the paddle left in Pong (decrements b) and steers left in Night Driver. The label appears inverted relative to screen coordinates.