Temp Conversion Problem 2

This program performs bidirectional temperature conversion between Celsius and Fahrenheit. It presents a menu allowing the user to select C-to-F conversion (option 1), F-to-C conversion (option 2), or program termination (option 3). The C-to-F formula is implemented as (9*C+160)/5, an algebraically equivalent rearrangement of the standard (9/5)*C+32 that avoids floating-point division by 5 until the final step. An error counter variable E tracks invalid menu inputs, terminating the run after more than three mistakes, while a case counter K numbers each successful conversion.

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Program Analysis

Program Structure

The program is organised into several distinct regions separated by line number ranges:

1. Lines 10–160: Title banner display using TAB(15) to centre a boxed heading.
2. Lines 160–310: Initialisation and main menu loop, including error handling for invalid input.
3. Lines 320–390: Celsius-to-Fahrenheit conversion branch.
4. Lines 400–470: Fahrenheit-to-Celsius conversion branch.
5. Lines 480–600: Error termination and normal stop.
6. Lines 610–620: Save and re-run utilities.

Conversion Formulae

Both conversions avoid dividing by a non-integer early in the calculation, keeping intermediate values as integers where possible:

Direction	Formula Used	Standard Form
C → F	(9*C+160)/5	(9/5)*C + 32
F → C	(5*F-160)/9	(5/9)*(F − 32)

The rearrangement multiplies through by the denominator before adding the offset (32 × 5 = 160), deferring the division to a single operation. This is a clean algebraic optimisation that also happens to reduce floating-point rounding on integer inputs.

Error Handling

Variable E counts invalid menu entries. After each bad input at line 270, E is incremented and checked against 3. The check at line 280 is duplicated at line 300, which is redundant — control can never reach line 300 if E>3 because line 280 would have already branched to 480. This double-check is a minor anomaly but causes no functional problem.

Case Counter

Variable K is incremented at the start of each conversion branch (lines 320 and 400) and printed as a running case number. It is initialised to 0 at line 170 alongside E, ensuring a clean slate each time the program runs from the top. The menu loop (line 390 and 470) returns to line 180 rather than line 230, so the menu prompt is reprinted in full for each new conversion, which is intentional for clarity.

Key BASIC Idioms

• Numeric INPUT for the menu choice (Q) rather than string input — any non-numeric entry would cause an error rather than being caught by the E counter.
• GOTO 180 after each conversion loops back to re-print the menu, effectively making the program re-entrant without a structured loop construct.
• Lines 610–620 (SAVE followed by RUN) are a common utility tail found in distributed listings, allowing the program to save itself and immediately restart.

Bugs and Anomalies

• Non-numeric input for Q, C, or F will cause a BASIC error rather than a graceful message, since INPUT is used without string validation.
• The duplicate check at lines 280 and 300 is logically redundant (see Error Handling above).
• The apostrophe in the termination message at line 480 reads I/M SORRY — this is a typo for I'M, as the apostrophe character is not directly available in the standard character set and has been substituted with a forward slash.
• There is a large gap between line 270 (LET E=E+1) and line 480 (termination message) — lines 600 follows 490 directly, skipping line numbers 500–599; line 500 is referenced by line 260 for normal termination but does not exist, which would cause a “line does not exist” error if the user types 3.