Multiplication Tables

This program displays multiplication tables for a user-chosen number, printing the series from 1× to 10× in a formatted layout. After displaying the table, it prompts the user to try another and loops back unless “NO” is entered. The condition `IF NOT A$=”NO”` is a characteristic Sinclair BASIC idiom where `NOT` applies to the entire string comparison, returning 1 (true) if the strings are not equal. The double commas in line 12 (`PRINT ,,J`) use comma column-tabbing to position output across the screen. The program includes a SAVE command with an auto-run flag embedded in the filename.

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Program Analysis

Program Structure

The program is divided into three logical phases: an introduction/input screen (lines 1–3), the table display loop (lines 10–13), and a replay prompt with conditional branching (lines 14–21). Line 30 halts execution cleanly with STOP, while lines 40 and 45 are utility lines for saving and auto-running.

1. Introduction (lines 1–3): Titles the program and solicits the multiplier via INPUT A.
2. Table display (lines 10–13): A FOR loop from 1 to 10 prints each multiplication result.
3. Replay logic (lines 14–21): Prompts for another try, branching back to line 2 unless the user types “NO”.

Key BASIC Idioms

Line 12 uses PRINT ,,J;" X ";A;" = ";A*J. The two leading commas advance the print position by two tab columns before printing the expression, giving the output a centred appearance on a 32-column display. This is a common Sinclair BASIC spacing trick.

Line 19 uses IF NOT A$="NO" THEN GOTO 2. In Sinclair BASIC, NOT has lower precedence than the relational operator, so this evaluates as IF NOT (A$="NO") — i.e., loop back unless the user typed exactly “NO”. This idiom is idiomatic but can surprise programmers expecting C-style logical-NOT behaviour.

Line 2 uses a single PRINT statement with a comma-separated string to print on two consecutive lines, a standard Sinclair multi-line print shorthand.

Program Flow Table

Lines	Purpose
1–3	Title display and initial multiplier input
10–13	FOR loop printing the ×1 to ×10 table
14–17	Prompt and input for replay decision
18–19	CLS and conditional branch back to line 2
21	Farewell message
30	STOP
40	SAVE with auto-run flag
45	RUN (executed if program is loaded without auto-run)

Notable Techniques

• The loop variable is J (line 11), while the multiplier is A (line 3), keeping variable names distinct and avoiding shadowing.
• The replay loop reuses the INPUT A$ at line 17 without re-displaying the full title (line 1), branching directly to line 2 to re-prompt for a new table number — a minor UX economy.
• Line 21 uses PRINT AT 21,0;, with a trailing comma before the string, which tabs to the next print zone before outputting the farewell, centering it roughly on screen.

Bugs and Anomalies

• The replay check is case-sensitive: entering “no” or “No” will cause the program to loop back rather than exit, which may surprise users.
• There is no validation of the INPUT A value — entering 0 or a non-numeric value will either produce trivial output or cause an error.
• Line 14 uses PRINT AT 20,0, which may overlap table output if 10 rows of data have scrolled or if the screen has not been cleared since the previous iteration; however, the CLS at line 10 ensures a clean display at the start of each table.