---
title: "Temperature Conversion"
id: 57021
type: "computer_media"
slug: "temperature-conversion"
url: "http://localhost/computer_media/temperature-conversion/"
markdown_url: "http://localhost/computer_media/temperature-conversion.md"
published_at: "2024-10-02T07:43:54+00:00"
modified_at: "2026-04-03T07:58:44+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/45_Temp.png"
excerpt: "A two-way temperature converter with a subtle but consequential arithmetic bug hiding in one of its conversion subroutines — can you spot it?"
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: "Science"
    slug: "science"
    taxonomy: "genre"
    url: "http://localhost/type/science/"
media_contents:
  - id: 56732
    title: "Timex Sinclair Public Domain Library Tape 1001"
    type: "computer_media"
    url: "http://localhost/computer_media/timex-sinclair-public-domain-library-tape-1001/"
media_type: "Program"
mediadate: "198x"
images:
  - url: "http://localhost/wp-content/uploads/2024/10/45_Temp.png"
media_type_tags: "Science"
---

# Temperature Conversion

This program performs bidirectional temperature conversion between Celsius and Fahrenheit. At startup the user chooses which direction to convert; Celsius-to-Fahrenheit conversions use the subroutine at line 1000 (formula F = (9/5)×C + 32), while Fahrenheit-to-Celsius conversions use the subroutine at line 2000. After each conversion the user is asked whether they are finished, allowing repeated conversions in a loop via GOTO. The program contains a notable bug at line 2010: the Fahrenheit-to-Celsius formula incorrectly subtracts 12 instead of 32, giving C = (F−12)×(5/9) rather than the correct C = (F−32)×(5/9).

***

## Program Analysis

### Program Structure

The program is divided into three logical regions: a main menu and dispatch block (lines 5–120), a Celsius-to-Fahrenheit subroutine (lines 1000–1030), and a Fahrenheit-to-Celsius subroutine (lines 2000–2030). Lines 3000–3010 handle saving and restarting the program.

1. **Lines 5–11:** Title display.
2. **Lines 20–30:** User selects conversion direction; branching on `A$="Y"` jumps to the C→F path at line 80.
3. **Lines 40–75:** F→C loop: prompts for Fahrenheit input, calls `GOSUB 2000`, asks if finished, repeats or stops.
4. **Lines 80–120:** C→F loop: prompts for Celsius input, calls `GOSUB 1000`, asks if finished, repeats or stops.
5. **Lines 1000–1030:** Subroutine — computes and prints Celsius-to-Fahrenheit conversion.
6. **Lines 2000–2030:** Subroutine — computes and prints Fahrenheit-to-Celsius conversion.

### Conversion Formulas

| Subroutine | Line | Formula Used | Correct Formula | Status |
| --- | --- | --- | --- | --- |
| C → F | 1010 | `F=(9/5)*C+32` | F = (9/5)×C + 32 | ✓ Correct |
| F → C | 2010 | `C=(F-12)*(5/9)` | C = (F−32)×(5/9) | ✗ Bug: −12 should be −32 |

### Bug: Incorrect Fahrenheit-to-Celsius Constant

Line 2010 reads `LET C=(F-12)*(5/9)`. The correct offset is 32, not 12. This means every Fahrenheit-to-Celsius result will be wrong; for example, 32°F would yield approximately 11.1°C instead of the correct 0°C. The C→F subroutine at line 1010 is correct, making the error asymmetric.

### Key BASIC Idioms and Techniques

- **GOSUB/RETURN structure:** Conversion logic is cleanly separated into subroutines at lines 1000 and 2000, keeping the main loop concise.
- **Input echo:** Lines 42 and 82 each `PRINT` the just-entered value immediately after `INPUT`, providing visual confirmation of the entered number.
- **Y/N loop control:** Continuation is handled by testing for `"N"` rather than `"Y"` — the program exits on anything other than an explicit “N”, meaning any unexpected input also terminates the loop gracefully via `STOP`.
- **Variable reuse:** The variable `C` serves double duty — it holds the Celsius input in the main block and is also written by the F→C subroutine at line 2010. Equally, `F` is used both as direct input and as output from the C→F subroutine. This creates no conflict given the program’s linear flow but could cause issues if the structure were extended.

### Notable Anomalies

- The program uses three separate input variables for the Y/N prompts (`A$`, `B$`, `C$`) where a single variable would suffice, slightly inflating memory use.
- Line 11 uses a bare `PRINT` to emit a blank line — a standard idiom for spacing output.
- The label in the `SAVE` command at line 3000 is an unusual alphanumeric string (`"1004%5"`), suggesting a filing or catalogue convention rather than a descriptive name.

## Source Code

```
   5 REM TEMP CONVERSION
  10 PRINT "TEMPERATURE CONVERSION"
  11 PRINT 
  20 PRINT "DO YOU WISH TO CONVERT C TO F(Y/N)"
  21 INPUT A$
  30 IF A$="Y" THEN GOTO 80
  40 PRINT "ENTER DEGREES F"
  41 INPUT F
  42 PRINT F
  50 GOSUB 2000
  60 PRINT "ARE YOU FINISHED(Y/N)"
  61 INPUT B$
  70 IF B$="N" THEN GOTO 40
  75 STOP 
  80 PRINT "ENTER DEGREES C"
  81 INPUT C
  82 PRINT C
  90 GOSUB 1000
 100 PRINT "ARE YOU FINISHED(Y/N)"
 101 INPUT C$
 110 IF C$="N" THEN GOTO 80
 120 STOP 
 1000 REM CEL TO FAHR CONV
 1010 LET F=(9/5)*C+32
 1020 PRINT C;" DEGREES CELSIUS=   ";F;" DEGREES FAHRENHEIT"
 1030 RETURN 
 2000 REM FAHR TO CEL CONV
 2010 LET C=(F-12)*(5/9)
 2020 PRINT F;" DEGREES FAHRENHEIT=  ";C;"  DEGREES CELSIUS"
 2030 RETURN 
 3000 SAVE "1004%5"
 3010 RUN
```