---
title: "Crack Safe"
id: 50607
type: "computer_media"
slug: "crack-safe"
url: "http://localhost/computer_media/crack-safe/"
markdown_url: "http://localhost/computer_media/crack-safe.md"
published_at: "2023-06-23T11:26:00+00:00"
modified_at: "2026-03-30T21:41:34+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2019/02/20230809-041332.jpg"
excerpt: "Guess three secret numbers to crack a combination safe, guided by musical pitch hints, before your security units run out."
category:
  - name: "Archived Media"
    slug: "archived-media"
    taxonomy: "category"
    url: "http://localhost/category/archived-media/"
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "TS 2068"
    slug: "ts2068"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts2068/"
model:
  - name: "Timex/Sinclair 2068"
    slug: "ts-2068"
    taxonomy: "model"
    url: "http://localhost/model/ts-2068/"
genre:
  - name: "Game"
    slug: "game"
    taxonomy: "genre"
    url: "http://localhost/type/game/"
media_type: "Program"
download_url: "https://archive.org/download/timex-sinclair-software-archive/Crack%20Safe%20%28198x%29%28TS2068%29%28US%29%28Program%29.zip"
mediadate: "198x"
images:
  - url: "http://localhost/wp-content/uploads/2023/06/SCR-20260329-prfp.png"
media_type_tags: "Game"
---

This program simulates a combination lock safe-cracking game in which the player must guess three secret numbers between 1 and 50. The screen displays a graphical safe door drawn with PLOT, DRAW, and CIRCLE commands, including concentric filled circles for a dial effect using INK 0 and INVERSE. As the player dials each number, a BEEP sequence plays with pitch values calculated from a parabolic curve centered on the target number, providing an audio hint about proximity. The player starts with 10 security units, losing one for each incorrect guess; reaching zero triggers a flashing security alert and a 50-note alarm loop before halting.

***

## Program Analysis

### Program Structure

The program is organized into three distinct phases: screen setup and graphics (lines 5–45), the main game loop across three combinations (lines 50–200), and the endgame resolution (lines 210–220). The outer `FOR c=1 TO 3` loop at line 50 controls the three combination stages, with a shared input/validation/feedback cycle inside it.

### Screen and Graphics Setup

Lines 5–8 paint a green background and white inner panel, then use `PLOT`/`DRAW` to draw a rectangular border at pixel coordinates (64,23) with dimensions 127×128. Lines 15–20 draw the safe dial: a solid ring of concentric circles in INK 1 (blue) for radii 25–45, then a smaller filled circle in INK 0 (black) for radii 56–64 to erase the center, giving a donut appearance. Line 40 draws solid block-graphic borders down the left and right edges using the `\::` (█) escape character.

### Combination and Pitch Calculation

At line 60, each secret number `n` is chosen randomly: `INT(RND*46+5)`, giving a range of 5–50. Line 70 populates the 50-element array `b()` with pitch values using a piecewise linear formula centered on `n`:

- For `i < n`: pitch = `25 - (n-1)/2` (a constant below target, scaled)
- For `i > n`: pitch = `25 - (i-n)/2` (decreasing above target)
- For `i = n`: pitch is set to `-10` (a distinct low note marking the exact target)

The Boolean arithmetic `(i<n)` and `(i>n)` evaluate to -1 (true) or 0 (false) in Spectrum BASIC, so the expression correctly selects the appropriate branch without an `IF` statement — a classic Sinclair idiom.

There is a subtle anomaly in the formula: the `i < n` branch evaluates to `25 - (n-1)/2` regardless of `i`, making all positions below the target play the same pitch. This means the audio hint is asymmetric: the pitch only changes as the dial passes above the target number.

### Dial Animation

Lines 100–120 animate the dial movement. The loop `FOR k=x TO d STEP 1-2*(d<x)` sweeps from the current position `x` to the entered number `d`, stepping +1 or -1 depending on direction. Each step plays `BEEP 0.1,b(k)`, giving an audible sweep across the pitch array. After the sweep, `x` is updated to `d`.

### Input Validation

Line 90 rejects values outside 1–50 or equal to the current dial position (`d=x`), displaying a flashing “UNAUTHORIZED ENTRY” message and immediately setting `su=0` to trigger the alarm. Line 80 uses `INPUT FLASH 1;` to present a flashing prompt. The condition `d=x` prevents re-entering the current number, simulating the requirement to move the dial.

### Security Units and Endgame

The player starts with `su=10` security units (line 10). Each wrong guess decrements `su` at line 160. A warning message appears at line 180 when only one unit remains. Reaching zero sends the program to line 210, where a 50-iteration double-beep alarm plays before `STOP`. Completing all three combinations sends control past line 200’s `NEXT c` to line 210, where the `IF su=0` check is false, so execution falls through to the congratulatory message at line 220.

### Notable Techniques

- Boolean expressions used as numeric values in arithmetic (lines 70, 110) — a hallmark Sinclair BASIC optimization avoiding `IF` branches inside tight loops.
- Two-digit display padding at line 125: if `d < 10`, a leading zero is printed manually by printing `0` then `d` at the same position.
- Ascending confirmatory beeps on successful unlock (line 140): `FOR i=1 TO c: BEEP 0.5,-5*i` plays `c` descending-pitch tones, distinguishing first, second, and third unlocks audibly.
- The array `b(50)` is declared with `DIM b(50)` at line 10 but indexed 1–50, which is correct for Spectrum BASIC (1-based arrays).

### Potential Bugs and Anomalies

- The pitch formula for positions below `n` is constant (does not vary with `i`), so the audio feedback is one-sided. This may be intentional to increase difficulty, but it appears to be a mathematical oversight in the formula.
- If `d = n` on a correct guess, line 115’s `NEXT k` will attempt to continue the loop after line 110’s `FOR k`, which is fine structurally, but the `b(n)=-10` pitch will play as part of the sweep — the distinctive “click” note occurs at the target number during the sweep itself, which is a nice side effect.
- The variable `l` used in lines 5 and 7 is reused as a loop variable, but since these loops complete before `l` is needed again, there is no conflict.

## Source Code

```
    5 PAPER 5: FOR l=1 TO 21: PRINT TAB 31: NEXT l
    7 FOR l=3 TO 18: PRINT BRIGHT 1; PAPER 7;AT l,8;"                ": NEXT l
    8 PLOT 64,23: DRAW 0,128: DRAW 127,0: DRAW 0,-128: DRAW -127,0
   10 DIM b(50): LET x=50: LET su=10: LET cx=127: LET cy=87
   15 FOR r=25 TO 45: CIRCLE INK 1,cx,cy,r: NEXT r
   20 FOR r=56 TO 64: CIRCLE INK 0,cx,cy,r: NEXT r: INVERSE 1
   30 PRINT AT 0,0;"     CRACK THE COMBINATION      "
   35 PRINT AT 21,0;"                                ": INVERSE 0
   40 FOR i=1 TO 20: PRINT AT i,0;"\::";AT i,31;"\::": NEXT i
   45 PRINT AT 3,15;50
   50 FOR c=1 TO 3
   60 LET n=INT (RND*46+5)
   70 FOR i=1 TO 50: LET b(i)=25-(i<n)*(n-1)/2-(i>n)*(i-n)/2: NEXT i
   75 LET b(n)=-10
   80 INPUT FLASH 1;"Enter next number:";d
   90 LET d=INT d: IF d<1 OR d>50 OR d=x THEN PRINT INK 2; FLASH 1;AT 10,7;"UNAUTHORIZED ENTRY": LET su=0: GO TO 210
  100 PRINT PAPER 4; FLASH 1;AT 3,15;"--"
  110 FOR k=x TO d STEP 1-2*(d<x): BEEP 0.1,b(k)
  115 NEXT k
  120 PRINT AT 3,15;d: LET x=d
  125 IF d<10 THEN PRINT AT 3,15;0;d
  130 IF d<>n THEN GO TO 160
  140 FOR i=1 TO c: BEEP 0.5,-5*i: NEXT i
  150 PRINT AT 10,7;"Section ";c;" unlocked": GO TO 200
  160 LET su=su-1: PRINT AT 20,1;"You have ";su;" security units left."
  170 IF su=0 THEN PRINT AT 10,0; INK 2; FLASH 1;"** SECURITY ALERT - INTRUDER **": GO TO 210
  180 IF su=1 THEN PRINT AT 15,12; PAPER 2; FLASH 1;"Warning!"
  190 GO TO 80
  200 NEXT c
  210 IF su=0 THEN FOR i=1 TO 50: BEEP 0.5,10: BEEP 0.5,20: NEXT i: STOP 
  220 PRINT AT 15,0; PAPER 2; INK 7;"Well done!  You have opened the safe with ";su;" turns to spare!": STOP
```