Media Money

This program calculates and compares the Cost Per Mille (CPM) — the cost per 1,000 impressions — for two advertising media, such as newspapers or magazines. The user enters a name, ad cost, and circulation figure for each medium; the program divides cost by circulation and multiplies by 1,000 to produce the CPM for each. It then prints both CPM values and identifies which medium offers the lower cost, or reports no difference if they are equal. After displaying results, it waits for a keypress and loops back to accept new inputs.

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Program Analysis

Program Structure

The program is straightforward and linear, divided into three functional phases:

1. First medium input (lines 10–100): Prompts for name (N$), ad cost (A), and circulation (C); computes CPM as M = 1000 * (A / C).
2. Second medium input (lines 110–200): Repeats the same process for variables P$, Q, R, and S.
3. Results and loop (lines 210–350): Displays both CPM values, compares them with three IF statements, waits for a keypress, clears the screen, and loops back to line 10.

CPM Calculation

The core formula at lines 100 and 200 is standard advertising mathematics: multiply the ratio of cost to circulation by 1,000 to give the cost per thousand readers or viewers. The parentheses around A/C are redundant but harmless, as division already has higher precedence than multiplication.

Key Variables

Variable	Meaning
N$	Name of first medium
A	Ad cost for first medium
C	Circulation of first medium
M	CPM for first medium
P$	Name of second medium
Q	Ad cost for second medium
R	Circulation of second medium
S	CPM for second medium

Notable Techniques

• Keypress wait loop: Line 330 uses IF INKEY$="" THEN GOTO 330, a standard busy-wait idiom for pausing execution until any key is pressed.
• Three-way comparison: Lines 250–270 use three separate IF statements testing S>M, M>S, and M=S to cover all cases. This is idiomatic for BASIC dialects lacking ELSE or SELECT CASE.
• Continuous loop: The program never truly ends during normal use; line 350 sends execution back to line 10 after each comparison, allowing repeated use without restarting.

Bugs and Anomalies

• Line 140 typo: POKE "AD COST: $ "; should almost certainly be PRINT "AD COST: $ ";. As written, the POKE keyword expects two numeric arguments (an address and a value), so this line would produce a syntax or type error at runtime. This is evidently a transcription error in the listing.
• Unreachable lines 375–500: Lines 375 (CLEAR), 400 (SAVE "1001%5"), and 500 (RUN) are never reached during normal execution because the loop at line 350 returns to line 10 indefinitely. These lines exist solely for the user to GOTO or execute manually — the SAVE at line 400 stores the program with an auto-run flag encoded in the filename.
• Division by zero risk: If the user enters 0 for circulation, lines 100 or 200 will cause a division-by-zero error. No input validation is provided.