---
title: "Inducto"
id: 57425
type: "computer_media"
slug: "inducto"
url: "http://localhost/computer_media/inducto/"
markdown_url: "http://localhost/computer_media/inducto.md"
published_at: "2024-10-05T13:15:55+00:00"
modified_at: "2026-03-30T21:18:02+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/226_Indu.png"
excerpt: "A number-guessing game with a twist: instead of \"higher/lower,\" you get a mathematical clue — the square root of how far off your guess was."
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 1000"
    slug: "ts1000"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts1000/"
model:
  - name: "Timex/Sinclair 1000"
    slug: "ts-1000"
    taxonomy: "model"
    url: "http://localhost/model/ts-1000/"
genre:
  - name: "Game"
    slug: "game"
    taxonomy: "genre"
    url: "http://localhost/type/game/"
media_contents:
  - id: 56736
    title: "Timex Sinclair Public Domain Library Tape 1005"
    type: "computer_media"
    url: "http://localhost/computer_media/timex-sinclair-public-domain-library-tape-1005/"
media_type: "Program"
mediadate: "198x"
images:
  - url: "http://localhost/wp-content/uploads/2024/10/226_Indu.png"
media_type_tags: "Game"
---

# Inducto

INDUCTO is a number-guessing game that picks a secret integer between 1 and 20 and gives the player up to 10 attempts to identify it. After each wrong guess, instead of a simple “higher/lower” hint, the program reveals the square root of the absolute difference between the guess and the target, providing a scaled numeric clue. Line 20 uses a RND>RND comparison to introduce a probabilistic bias, giving a roughly 50% chance of re-rolling the target before play begins. The SCROLL command is used throughout to manage the limited display, keeping output readable on the small screen.

***

## Program Analysis

### Program Structure

The program is compact at 13 executable lines. Control flow is straightforward: a setup phase (lines 10–20), a guessing loop (lines 30–100), and a resolution phase (lines 110–150).

1. **Lines 10–20:** Generate the secret number `A` as a random integer 1–20. Line 20 re-rolls with roughly 50% probability.
2. **Lines 30–100:** A `FOR` loop over up to 10 guesses. Each iteration scrolls, prompts, reads input, and either branches to the win condition or prints a clue.
3. **Lines 110–150:** Print the answer, detect win vs. loss, and display the win message or `STOP`.
4. **Lines 160–170:**`SAVE` followed by `RUN` for tape storage and restart.

### The RND>RND Re-roll (Line 20)

Line 20 reads `IF RND>RND THEN GOTO 10`. Because two independent `RND` calls are evaluated, there is approximately a 50% chance of looping back to re-generate `A`. This does not produce a uniform distribution over iterations — it simply adds a non-deterministic delay before play starts, and the final value of `A` is still uniformly drawn from 1–20. It does not improve randomness in any meaningful way but is a common idiom seen in early BASIC games.

### The Clue Mechanic

Line 90 is the most distinctive feature of the game:

`PRINT "WRONG ";C,"CLUE- ";SQR(ABS(A-C))`

Rather than a binary higher/lower hint, the player receives `SQR(ABS(A-C))` — the square root of the absolute difference. For a range of 1–20, the maximum possible raw difference is 19, giving a maximum clue of approximately 4.36. This compresses the hint into a non-linear scale, making nearby misses hard to distinguish from each other (e.g., a difference of 1 yields clue 1.0, while a difference of 4 yields only 2.0), which increases difficulty compared to a direct difference hint.

### Win/Loss Detection

When the correct answer is entered, line 80 jumps to line 110, bypassing `NEXT B`. At line 130, the condition `C<>A` catches the case where the loop exhausted all 10 guesses without a correct answer — in that path `C` still holds the last (wrong) guess, so `STOP` is executed. If the player won, `C=A` and execution falls through to line 140, which prints the congratulatory message including `B`, the guess number on which they succeeded. Note the deliberate zero in `"W0W"` (digit zero, not letter O) — a common typographical quirk in early BASIC listings.

### Display Management

`SCROLL` is called at lines 40, 70, and 110 to advance the display before printing, preventing the “scroll?” prompt from interrupting gameplay on the ZX81’s 24-line limit.

### Notable Anomalies

- Line 120 ends with a trailing comma: `PRINT A,`. This positions the cursor at the next print zone rather than a new line, so the win message on line 140 prints on the same line as the revealed answer — a minor layout quirk.
- In the loss path (loop exhausted), `A` is printed at line 120 but the player’s last guess `C` is not re-displayed, which is slightly inconsistent with the win path where `B` is shown.
- The `RND>RND` idiom at line 20 is probabilistically inelegant; a simple `GOTO 10` with no condition, or no re-roll at all, would be functionally equivalent for randomness quality.

### Variable Summary

| Variable | Purpose |
| --- | --- |
| `A` | The secret target number (1–20) |
| `B` | Current guess number (loop counter, 1–10) |
| `C` | Player’s current guess (INPUT) |

## Source Code

```
   5 REM "INDUCTO"
  10 LET A=INT (RND*20)+1
  20 IF RND>RND THEN GOTO 10
  30 FOR B=1 TO 10
  40 SCROLL 
  50 PRINT "GUESS NO. ";B
  60 INPUT C
  70 SCROLL 
  80 IF C=A THEN GOTO 110
  90 PRINT "WRONG ";C,"CLUE- ";SQR (ABS (A-C))
 100 NEXT B
 110 SCROLL 
 120 PRINT A,
 130 IF C<>A THEN STOP 
 140 PRINT "W0W,YOU GOT IT MAN";B
 150 STOP 
 160 SAVE "1022%6"
 170 RUN
```