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.

Appears On

Timex Sinclair Public Domain Library Tape 1001

Tape 1001 of the Timex Sinclair Public Domain Library. Assembled by Tim Ward from many sources.

Image Gallery

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 

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