Four Arithmetic Tables

This program prints all four arithmetic operation tables (multiplication, division, addition, and subtraction) for the integers 1 through N, where N is entered by the user. It validates the input to ensure N is a positive integer before proceeding, rejecting non-integers and values ≤ 0. Each operation pair is displayed side by side in two columns using the comma separator in PRINT to align output. The tables are generated with nested FOR loops, with outer loops over I (or K) and inner loops over J (or L), printing all N×N combinations.

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Program Analysis

Program Structure

The program is straightforward and linear, divided into clearly demarcated sections:

1. Lines 100–150: Title banner displayed with asterisk borders.
2. Lines 160–200: Input loop with validation for a positive integer N.
3. Lines 210–300: Nested loops generating the multiplication and division tables.
4. Lines 310–400: Nested loops generating the addition and subtraction tables.
5. Line 500: STOP to end normal execution.
6. Lines 510–520: SAVE and RUN — utility lines appended after the logical end of the program.

Input Validation

Line 180 uses the expression N=INT(N) AND N>0 to ensure the entered value is both a whole number and positive. If either condition fails, an error message is printed at line 190 and control loops back to line 160 to re-prompt. This is a clean validation idiom for the platform.

Table Generation

Both table pairs use the same nested-loop structure. Variables I and J drive the multiplication/division block (lines 230–300), while K and L drive addition/subtraction (lines 330–400). The separation into distinct variable sets is a deliberate stylistic choice to keep sections independent, though reusing I and J would have been equally valid.

A PRINT with no arguments at lines 240 and 340 inserts a blank line between each outer-loop iteration, grouping the inner results for readability.

Column Layout

Each PRINT statement at lines 280 and 380 uses a comma to separate two expressions, which causes the second expression to print at the next print zone (column 32 on a standard display). This places the two operation results side by side. The headers at lines 210–220 and 310–320 use the same comma-separated technique to align column headings with the data below them.

Notable Techniques and Idioms

• Intermediate results P, Q, A, and D are computed into variables before printing rather than inline in the PRINT statement, improving readability at a minor memory cost.
• The STOP at line 500 cleanly terminates execution before the trailing SAVE/RUN lines, ensuring they are never reached during normal program flow.

Potential Issues

• Division by zero: When J=1 and I=0 could occur in theory, but the validation at line 180 ensures N>0, and both loops start at 1, so J is never 0. No division-by-zero risk exists.
• For large values of N, output will be very long and may scroll off screen before the user can read it. There is no pause mechanism between pages.
• Negative subtraction results (when K<L) are handled naturally by the arithmetic, so D can be negative — this is correct behaviour but may surprise younger users expecting a “larger minus smaller” table.

Variable Summary

Variable	Purpose
N	User-supplied upper bound for all tables
I, J	Outer and inner loop counters for multiplication/division
P	Product I×J
Q	Quotient I/J
K, L	Outer and inner loop counters for addition/subtraction
A	Sum K+L
D	Difference K−L