Real Estate

Real Estate Programs is a menu-driven financial calculator suite offering eight mortgage and property analysis tools, including monthly payment computation, full amortization schedules, remaining balance, accelerated payments, balloon payments, affordable house calculation, mortgage with second, and rental property analysis. The menu dispatch at line 185 uses an arithmetic expression combining the selected menu index with conditional offsets to compute the target subroutine address directly in a GO SUB statement, avoiding a lookup table or series of IF statements. Input is collected into a numeric array P() via a reusable INPAR subroutine that increments a parameter counter K, and string arrays X$() and Q$() handle menu labels and dialog prompts respectively. The amortization schedule loop at lines 665–695 rounds each month’s interest, principal, and balance to cents using INT with a 0.5 offset. A tight INKEY$ polling loop handles all keyboard input throughout, with separate routines for single-character entry and yes/no responses.

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Program Structure

The program is organized as a collection of named subroutines, each anchored at a round line number. A top-level loop at lines 100–190 initializes the menu, presents it, collects a choice, and dispatches to the appropriate module. After each module returns, execution loops back to line 100 for reinitalization.

Line Range	Label / Role
100–190	Main loop: menu setup and dispatch
235–255	Payment calculation subroutine (annuity formula)
275–330	Shared data-entry for amount, rate, term
375–390	Balance reduction loop (N months)
405–460	Module 1: Monthly Payment
605–725	Module 2: Mortgage Schedule
2200–2235	ANOTH – “Again?” prompt
3000–3030	DIALOG – three-line status/prompt display
3800–3830	INCH – single-character input via INKEY$
4200–4240	INIT – CLS, title, DIM arrays
4400–4440	INPAR – prompt and read one parameter into P(K)
4600–4690	MENU – display choices, validate selection
4800–4845	PAUSE – “press any key” routine
5400–5435	YES-NO – accept only Y or N via INKEY$
6635	Orphaned GO SUB 4400 with no enclosing module

Menu Dispatch Technique

Line 185 is the most distinctive feature of the program:

GO SUB X*200+(200 AND X<5)+(300 AND X>4)

This computes the target subroutine address arithmetically from the user’s menu choice X. For choices 1–4, the offset is X*200+200, producing addresses 400, 600, 800, and 1000. For choices 5–8, the offset is X*200+300, yielding 1300, 1500, 1700, and 1900. This avoids a chain of IF … GO SUB statements and doubles as a compact dispatch table, though it requires the modules to be placed precisely at those line numbers.

Parameter Input System

User inputs are stored in the numeric array P(10). The subroutine INPAR (line 4400) uses a global counter K to index successive entries: it displays the prompt stored in Q$(3), reads a value into P(K), echoes it on screen with PRINT AT, and increments K. Callers set K=1 before the first call and update Q$(3) before each call. This makes adding or reordering inputs straightforward.

Dialog / Prompt System

All user-facing messages use a three-slot string array Q$(3,32). The DIALOG subroutine (line 3000) prints a separator line followed by the concatenation of Q$(1), Q$(2), and Q$(3) on consecutive screen rows. Modules load these slots before calling GO SUB 3000 directly or via INPAR/ANOTH, giving a uniform look to every prompt without duplicating PRINT statements.

Penny-Rounding Arithmetic

Financial values are rounded to the nearest cent throughout using the standard idiom:

INT(value * 100 + 0.5) / 100

This appears at line 439 for the monthly payment result, and at lines 670, 675, and 680 inside the amortization schedule loop to keep interest, principal, and balance figures consistent across iterations.

INKEY$ Input Loops

Three distinct routines handle keyboard input without using INPUT for single keypresses:

• INCH (3820–3825): tight poll on INKEY$ until a non-empty character arrives, stored in C$.
• YES-NO (5415–5430): polls until exactly “Y” or “N” is pressed, stored in Y$.
• PAUSE (4835–4840): polls until any key is pressed, stored in Z$.

The MENU routine calls INCH and converts the result with VAL C$, treating “0” as choice 10 for a potential tenth menu option.

Array Reinitialization

The INIT subroutine (line 4200) calls DIM X$(10,28), DIM Q$(3,32), and DIM P(10) every time a new module is entered via the main loop. This clears all arrays to empty/zero before each module populates them, preventing stale values from a prior run. It is a simple but effective reset strategy.

Notable Anomalies

• Line 6635 (GO SUB 4400) appears in isolation with no surrounding module code. It is likely a fragment of an unfinished or partially deleted module.
• The MENU subroutine (lines 4605–4610) contains a FOR J=1 TO 10 … NEXT J loop with no body, which serves only as a brief delay and has no functional effect on program logic.
• The listing includes REM comments at key subroutine entries (e.g., REM "ANOTH", REM "DIALOG") that serve as subroutine name labels, a common documentation convention when the language lacks named procedures.
• Several modules referenced by the dispatch formula (addresses 800, 1000, 1300, 1500, 1700, 1900) are absent from the provided listing, suggesting the listing is incomplete.