---
title: "Enigma"
id: 72040
type: "computer_media"
slug: "enigma"
url: "http://localhost/computer_media/enigma/"
markdown_url: "http://localhost/computer_media/enigma.md"
published_at: "2026-10-20T14:07:38+00:00"
modified_at: "2026-10-20T14:19:11+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2026/10/5_ENIGMA.png"
excerpt: "A number-reversal trick: subtract a number's reverse, then add the result to its own reverse, and see the total the arithmetic always produces."
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/"
indiv:
  - name: "Gene G. Buza"
    slug: "gene-g-buza"
    taxonomy: "indiv"
    url: "http://localhost/indiv/gene-g-buza/"
genre:
  - name: "Demo"
    slug: "demo"
    taxonomy: "genre"
    url: "http://localhost/type/demo/"
media_contents:
  - id: 72046
    title: "Synchro-Sette May 1984"
    type: "computer_media"
    url: "http://localhost/computer_media/synchro-sette-may-1984/"
media_type: "Program"
programmers:
  - name: "Gene G. Buza"
    slug: "gene-g-buza"
    taxonomy: "indiv"
    url: "http://localhost/indiv/gene-g-buza/"
mediadate: "1984"
images:
  - url: "http://localhost/wp-content/uploads/2026/10/5_ENIGMA.png"
media_type_tags: "Demo"
---

# Enigma

Demonstrates a number trick. Enter a number and the program reverses its digits, prints the difference between the number and its reverse, then reverses that difference and adds the two together. With most three-digit numbers whose first and last digits differ, the final total is always 1089.

***

## Program Analysis

The program is about twenty lines. The number is taken as a string so that it can be reversed character by character (lines 50–70), and `VAL` turns both forms back into numbers. The positive difference is worked out with two `IF` tests, turned into a string with `STR$`, reversed the same way and added to itself. `PAUSE 40000` waits for a key before the program restarts with `RUN`.

### Potential Issues

- If the number reads the same in both directions, neither `IF` at lines 110–120 sets `C`, so line 130 stops with an error on the first run and prints the previous value later.
- A two-digit difference such as 99 is reversed as “99” and not “990”, because the program does not pad it to three digits. Such numbers give 198 in place of 1089.

## Source Code

```
  10 PRINT "ENTER A NUMBER?"
  20 INPUT A$
  30 LET A=VAL A$
  40 LET B$=""
  50 FOR N=LEN A$ TO 1 STEP -1
  60 LET B$=B$+A$(N)
  70 NEXT N
  80 PRINT ,,,,"DIFFERENCE BETWEEN ";A$
  90 PRINT "AND ";B$;" IS:"
 100 LET B=VAL B$
 110 IF (A-B)>0 THEN LET C=A-B
 120 IF (B-A)>0 THEN LET C=B-A
 130 PRINT C
 140 LET C$=STR$ C
 150 LET D$=""
 160 FOR N=LEN C$ TO 1 STEP -1
 170 LET D$=D$+C$(N)
 180 NEXT N
 190 LET D=VAL D$
 200 PRINT ,,C;" + ";D;" = ";C+D
 210 PAUSE 40000
 220 CLS
 230 RUN 
9998 SAVE "ENIGM[A]"
9999 RUN
```