---
title: "Area of Circle"
id: 56999
type: "computer_media"
slug: "area-of-circle"
url: "http://localhost/computer_media/area-of-circle/"
markdown_url: "http://localhost/computer_media/area-of-circle.md"
published_at: "2024-10-02T07:19:45+00:00"
modified_at: "2026-03-30T21:20:20+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/23_Area.png"
excerpt: "A compact circle-area calculator using the built-in PI constant, hardwired to radius 5 — then it lists its own source code after saving."
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: 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/2024/10/23_Area.png"
media_type_tags: "Mathematics"
---

# Area of Circle

This program calculates the area of a circle using the formula A = π × R², with the radius hardcoded to 5 units. It stores π in the variable P via the built-in PI function and computes the area in a single LET statement. The result is printed as a formatted sentence labelling the output in square inches. After saving, the program executes a LIST command to display its own source code.

***

## Program Analysis

### Program Structure

The program is a straightforward linear sequence with no loops, branches, or subroutines. It runs from top to bottom in six executable lines:

1. `5` — REM comment identifying the program
2. `10` — assigns the built-in `PI` constant to variable `P`
3. `30` — hardcodes the radius as `R=5`
4. `40` — computes the area with `A=P*R*R`
5. `50` — prints the formatted result
6. `60` — saves the program
7. `70` — lists the program source

### Key BASIC Idioms

Storing `PI` in a single-letter variable `P` at line `10` is a common optimisation: referencing a numeric variable is marginally faster than evaluating the `PI` keyword repeatedly, though with only one use here the benefit is negligible. The area formula uses multiplication rather than exponentiation (`R*R` instead of `R^2`), which is slightly faster since the power operator involves a more expensive routine.

### Notable Techniques and Observations

- The line numbers skip non-uniformly (5, 10, 30, 40, 50, 60, 70) — line `30` follows `10` with a gap of 20, suggesting lines may have been deleted during development.
- The radius is hardcoded rather than prompted from the user via `INPUT`, making this a single-purpose demonstration rather than a general-purpose tool.
- The `PRINT` statement at line `50` mixes string literals and numeric output using semicolons, producing inline concatenation with the computed value `A` between two strings.
- Line `70` executes `LIST` as a program statement; this causes the interpreter to display the source listing after the `SAVE` completes, which is an unusual post-run behaviour.

### Bugs and Anomalies

There are no computational bugs. The formula `P*R*R` correctly implements πr². The output label “SQUARE INCHES” implies a fixed real-world unit, but since the radius is simply the abstract number 5 with no unit established in the code, this label is technically arbitrary.

## Source Code

```
   5 REM AREA OF CIRCLE
  10 LET P=PI
  30 LET R=5
  40 LET A=P*R*R
  50 PRINT "THE CIRCLE/S AREA IS ";A;"  SQUARE INCHES."
  60 SAVE "1002%3"
  70 LIST
```