Ad Profit

This program calculates advertising campaign profit, taking inputs for retail price, wholesale cost, advertising expenditure, and quantity sold. It then computes net profit using the formula E = A×B − A×C − D. A break-even mode is triggered when the user enters 0 for quantity sold, whereupon the program instead solves for the number of units required to achieve a desired profit target using the rearranged formula A = (F+D)/(B−C). The program loops continuously, clearing the screen and restarting the input sequence after each calculation.

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Program Analysis

Program Structure

The program is divided into clearly delineated functional blocks:

1. Lines 1–4: Title display and instructions
2. Lines 10–120: Input collection (retail price, wholesale cost, ad cost, quantity sold)
3. Line 130: Branch decision — normal profit vs. break-even mode
4. Lines 200–220: Normal profit calculation and display
5. Lines 300–350: Break-even unit calculation
6. Lines 400–450: Loop control — wait for keypress, clear screen, restart
7. Lines 475–600: Save and auto-run block (never reached in normal execution)

Key Variables

Variable	Meaning
B	Retail (list) price per unit
C	Manufacturing or wholesale cost per unit
D	Total advertising cost
A	Quantity sold (or computed break-even quantity)
E	Calculated profit
F	Desired profit (break-even mode input)

Profit Calculation

In normal mode (line 200), profit is computed as E = A*B - A*C - D, which represents total revenue minus total cost-of-goods minus fixed advertising spend. This could be simplified to E = A*(B-C) - D, but the expanded form is functionally correct.

In break-even mode (line 330), the formula is algebraically rearranged to A = (F+D)/(B-C), solving for the number of units needed. Entering 0 for profit wanted (F=0) gives the true break-even unit count.

Key BASIC Idioms

• The keypress-wait loop at line 430 uses IF INKEY$="" THEN GOTO 430, a standard polling idiom on this platform.
• Each INPUT statement is preceded by a PRINT prompt and followed by an echoing PRINT of the entered value, giving a clean audit trail on screen.
• The infinite main loop is driven by GOTO 10 at line 450 after a CLS, recycling the program without restarting it.

Notable Anomalies

• Lines 475 (CLEAR), 500 (SAVE), and 600 (RUN) are unreachable during normal execution; the loop at line 450 never falls through to them. They exist solely as a tape-saving convenience to be run manually.
• No input validation is performed: entering identical values for B and C (i.e., zero margin) in break-even mode causes a division-by-zero error at line 330.
• The PRINT A echo at line 120 prints the raw numeric value of the quantity entered rather than formatting it with a label, which is inconsistent with the labelled echoes used for B, C, and D.