Exam Score Sorting

This program collects exam scores one at a time and tallies them into letter-grade buckets (A through F), tracking the total count and the minimum and maximum scores entered. Input continues in a loop until the user types “X”, at which point results are displayed using PRINT with tab-formatted columns. Initialisation is handled via a GOSUB to line 400, which uses CLEAR to reset all variables before zeroing A, B, C, D, F, and N explicitly. The grade boundaries follow a standard 10-point scale: below 60 is F, 60–69 is D, 70–79 is C, 80–89 is B, and 90+ is A.

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Program Analysis

Program Structure

The program is divided into four logical sections:

1. Initialisation (lines 400–470): A subroutine called at startup via GOSUB 400 that clears variables and sets all counters to zero.
2. Input loop (lines 20–180): Repeatedly prompts for a score, classifies it, updates the running min/max, and loops back until “X” is entered.
3. Results display (lines 200–270): Prints total count, score range, and each letter-grade tally before halting with STOP.
4. Utility lines (500–600): A SAVE line and a bare RUN at line 600.

Grade Classification Logic

Each score is tested against five mutually exclusive ranges using consecutive IF statements on lines 100–140. The boundaries implement a standard 10-point letter-grade scale:

Grade	Condition	Counter
F	G < 60	F
D	G > 59 AND G < 70	D
C	G > 69 AND G < 80	C
B	G > 79 AND G < 90	B
A	G > 89	A

Using strict inequalities with integer boundary values (e.g. G > 59 AND G < 70) correctly handles whole-number scores, but would silently misclassify a fractional score such as 59.5, which falls into no bucket. This is a minor latent bug for non-integer inputs.

Min/Max Tracking

Lines 150 and 155 seed both the low (L) and high (H) variables with the very first score when N=1. Subsequent scores update L downward (line 160) and H upward (line 170). This is a clean idiom that avoids needing a sentinel value or a separate flag variable.

Initialisation Subroutine

The subroutine at line 400 begins with CLEAR, which on this platform erases all variables. The subsequent explicit assignments of A, B, C, D, F, and N to zero are therefore redundant — variables default to zero after CLEAR — but serve as readable documentation of the program’s state. The variable L and H are not initialised here; they are handled lazily at lines 150–155 on the first score entry.

Input Handling

The program accepts score input as a string (G$) and converts it with VAL G$ at line 60. The sentinel value “X” is tested at line 50 before the VAL conversion, correctly avoiding a numeric conversion error on non-numeric input. However, any non-numeric, non-“X” input would cause a VAL error at line 60; there is no general error trap.

Notable Techniques and Anomalies

• The title line (line 5) prints without a preceding CLS, but line 40 issues a CLS after each score entry, keeping the display clean during data entry.
• PRINT "A",A (and similarly for B–F) uses the comma tab stop to produce a two-column layout, aligning grade labels with their counts.
• Line 600 contains a bare RUN with no line number argument, which would restart the entire program from line 5 if ever reached — but it is unreachable during normal execution since line 270 halts with STOP.
• The program uses the variable name F for the fail-grade counter. Since F is not a reserved keyword in this BASIC dialect, this is valid, though it could cause confusion with numeric string functions in other contexts.