---
title: "Temperature Conversion"
id: 57284
type: "computer_media"
slug: "temperature-conversion-2"
url: "http://localhost/computer_media/temperature-conversion-2/"
markdown_url: "http://localhost/computer_media/temperature-conversion-2.md"
published_at: "2024-10-04T08:05:20+00:00"
modified_at: "2026-03-30T21:18:38+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/172_Temp.png"
excerpt: "A neat temperature converter that handles Fahrenheit, Celsius, and Kelvin with input validation and a clean display loop — all in under 20 lines of BASIC."
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: "Mathematics"
    slug: "mathematics"
    taxonomy: "genre"
    url: "http://localhost/type/mathematics/"
media_contents:
  - id: 56734
    title: "Timex Sinclair Public Domain Library Tape 1003"
    type: "computer_media"
    url: "http://localhost/computer_media/timex-sinclair-public-domain-library-tape-1003/"
media_type: "Program"
mediadate: "198x"
images:
  - url: "http://localhost/wp-content/uploads/2024/10/172_Temp.png"
media_type_tags: "Mathematics"
---

This program converts temperatures between Fahrenheit, Celsius, and Kelvin. The user enters a numeric temperature and selects a unit (F, C, or K); an input validation loop at line 70 rejects anything other than these three letters before proceeding. Two subroutines handle the conversions: lines 200–220 convert Fahrenheit to Celsius using the standard (T−32)×5/9 formula, while lines 300–340 handle both Celsius-to-Fahrenheit and Kelvin-to-Fahrenheit by first normalising Kelvin to Celsius before applying the C×9/5+32 formula. After displaying the result, the program waits for any key press via INPUT A$ before clearing the screen and looping back to the start.

***

## Program Analysis

### Program Structure

The program is organised into a main loop and two conversion subroutines:

1. **Lines 10–150**: Main loop — prompts for temperature and unit, dispatches to a subroutine, displays the result, waits for a keypress, then repeats.
2. **Lines 200–220**: Fahrenheit → Celsius subroutine.
3. **Lines 300–340**: Celsius or Kelvin → Fahrenheit subroutine.

### Conversion Logic

| Input unit | Subroutine | Formula | Output unit |
| --- | --- | --- | --- |
| F | 200 | (T − 32) × 5 / 9 | C |
| C | 300 | C × 9/5 + 32 | F |
| K | 300 | (T − 273) × 9/5 + 32 | F |

Note that Kelvin converts to Fahrenheit only; there is no direct K→C path presented to the user as a final result, though the intermediate Celsius value is computed in `C` at line 310.

### Input Validation

Line 70 implements a validation loop by re-routing to line 60 (`GOTO 60`) if the entered string is not one of the three accepted unit codes. This is a common BASIC idiom that keeps the user in a tight loop until valid input is received, without any explicit error message being printed.

### Key BASIC Idioms

- **Subroutine dispatch via consecutive IF statements**: Lines 90 and 100 each test `Q$` independently and call the appropriate `GOSUB`. Because the two conditions are mutually exclusive (validated at line 70), only one subroutine fires per pass.
- **Pause-via-INPUT**: Line 130 uses `INPUT A$` as a “press ENTER to continue” gate, a standard idiom where the variable `A$` is never actually used.
- **Shared subroutine for two input units**: The Kelvin branch shares the Celsius→Fahrenheit subroutine (line 300) by adjusting the intermediate variable `C` at line 310, avoiding code duplication.

### Notable Anomalies

- The Kelvin conversion uses 273 as the offset rather than the more precise 273.15. This introduces a small but non-trivial rounding error for scientific use.
- The program only converts in one direction per unit pair: F→C, C→F, and K→F. There is no C→K, K→C, or F→K path.
- Lines 350 and 360 (`SAVE "1017%2"` and `RUN`) appear to be a save-and-restart tail appended to the listing and are not part of the interactive program flow.

## Source Code

```
  10 REM "TEMP CONV"
  20 PRINT "ENTER TEMPERATURE"
  30 INPUT T
  40 PRINT T
  50 PRINT "C, F, OR K";
  60 INPUT Q$
  70 IF Q$<>"F" AND Q$<>"C" AND Q$<>"K" THEN GOTO 60
  80 PRINT Q$
  90 IF Q$="F" THEN GOSUB 200
 100 IF Q$="C" OR Q$="K" THEN GOSUB 300
 110 CLS 
 120 PRINT T;" ";Q$;"=";N;" ";R$
 130 INPUT A$
 140 CLS 
 150 GOTO 10
 200 LET N=(T-32)*5/9
 210 LET R$="C"
 220 RETURN 
 300 LET C=T
 310 IF Q$="K" THEN LET C=T-273
 320 LET N=C*9/5+32
 330 LET R$="F"
 340 RETURN 
 350 SAVE "1017%2"
 360 RUN
```