Checkbook Balancer

This program implements a checkbook balancing assistant that guides the user through reconciling their bank statement with their personal records. It collects outstanding check numbers and amounts, recent deposits not yet reflected on the statement, and the ending statement balance, then computes the reconciled balance using the formula: (statement balance + recent deposits) − outstanding checks. A rounding correction using INT(p*100+0.5)/100 ensures the final balance displays to two decimal places. The program uses an infinite FOR/NEXT loop idiom (FOR i=1 TO i) as a controlled input loop, exiting via GO TO when a sentinel value of zero is entered. Screen layout is managed with AT coordinates, and INVERSE, FLASH, PAPER, and OVER attributes are used for visual emphasis of totals and prompts.

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Program Analysis

Program Structure

The program is organized into a linear flow with two subroutine calls and a handful of input loops. Execution proceeds as follows:

1. Lines 20–140: Initialize variables, display a decorative banner via the subroutine at line 450, and present a four-step instruction screen with a flashing “Press any key” prompt.
2. Lines 150–270: Draw a red-papered left-column area for outstanding checks, then collect check numbers and amounts in a loop, accumulating a total t.
3. Lines 280–420: Collect the statement balance b and recent unposted deposits d, compute totals, and display the reconciliation layout on the right side of the screen.
4. Lines 430–445: Offer the user a choice to print a copy (COPY), restart, or re-prompt.
5. Lines 450–500: Subroutine that prints a decorative banner row of $$ characters (16 pairs).
6. Line 9999: A save/verify utility block not reached during normal execution.

Key BASIC Idioms

The program uses the well-known FOR i=1 TO i infinite loop idiom at lines 220 and 290. Because i is already set to 1 from a prior loop iteration (or initialized by the FOR statement itself), the loop condition is always satisfied, making it effectively infinite. Exit is achieved by a GO TO when the user enters the sentinel value 0. This avoids needing a pre-known count of entries while staying within standard BASIC.

The subroutine at line 450 is called with GO SUB 450 to print decorative separator lines. It uses a FOR/NEXT loop to print 16 pairs of $$, creating a dollar-sign banner, then returns. The line numbering jumps (450, 470, 490, 500) suggest earlier editing removed intermediate lines.

Rounding Technique

Line 380 applies a classic two-decimal rounding formula: LET p=INT(p*100+.5)/100. Multiplying by 100 shifts two decimal places, adding 0.5 before truncating via INT achieves standard rounding, and dividing by 100 restores the scale. This guards against floating-point artifacts that could produce results like 123.999999 instead of 124.00.

Screen Layout

The program divides the display into a left column (columns 0–13) for the outstanding checks list and a right column (columns 14–31) for the statement reconciliation. PAPER 1 (blue) is applied to the check area background. INVERSE 1 highlights the intermediate total and final balance labels. OVER 1 is used at lines 350 and 410 to draw underline-style separator marks using underscore characters without overwriting existing content.

Notable Techniques and Observations

• Variable reuse: a$ is reused at line 435 for the Copy/Again prompt, which is safe since the earlier use of a (numeric) for check amounts is complete by that point. However, a (numeric) and a$ (string) are distinct variables, so there is no conflict.
• Line 220 initializes the check-entry loop with FOR i=1 TO i; at this point i has not been explicitly set, so it defaults to 0. The FOR statement sets i=1 and compares to the limit, which is now also evaluated as 1, so the loop body executes once before the variable diverges — but because the exit is via GO TO 270, not NEXT i, the loop effectively runs indefinitely until the sentinel is entered.
• Line 110 contains “innumerical” (missing space between “in” and “numerical”) — a minor typographical error in the instruction text.
• The COPY command at line 440 sends a screen dump to a printer, a standard peripheral of the era.
• Line 9999 provides a self-contained tape save/verify sequence with BEEP prompts and is only reached manually, not during normal program execution.
• The FOR j=1 TO 22 loop at lines 160–180 paints 22 rows of the left column with PAPER 1 background before printing column headers, establishing the visual layout.

Variable Summary

Variable	Purpose
x	Current screen row for printing checks (starts at 3)
t	Running total of outstanding check amounts
d	Running total of recent unposted deposits
b	Statement ending balance entered by user
s	Subtotal: statement balance plus recent deposits
p	Final reconciled balance (rounded to 2 decimal places)
c	Check number entered by user
a	Check amount entered by user
r	Individual recent deposit amount
i	Loop counter (reused for both input loops)
j	Loop counter for painting background rows
a$	User response to Copy/Again prompt