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).

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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.