Tape Label

This program generates a formatted cassette tape label on a connected printer, allowing users to enter a tape title and up to 15 program names with index numbers for both Side A and Side B. The label is drawn entirely with Spectrum block graphics characters, creating a bordered two-column layout on screen before printing. The program uses OVER 1 mode to print text over the underline characters already drawn in the label cells. A POKE to address 23609 adjusts the printer line spacing, and the “STOP” detection at line 170 and 240 checks for a specific padded string that results from entering STOP (SYMBOL SHIFT + A) at an INPUT prompt.

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Program Analysis

Program Structure

The program is divided into four logical phases:

1. Setup (lines 10–17): Displays instructions, beeps, waits for ENTER, and POKEs the printer spacing system variable.
2. Label frame drawing (lines 20–110): Clears the screen, draws the tape label border using block graphics, and fills each row with underline characters for both columns.
3. Side A data entry (lines 120–200): Prompts for a tape title and up to 15 program entries with index numbers.
4. Side B data entry (lines 210–290): Mirrors the Side A entry loop for the right-hand column.

Label Drawing Technique

The border is built entirely from Spectrum block graphics escape sequences. Line 35 draws the top edge using ▖▀▀▀...▀▗ characters, and line 40 draws a solid double-pixel row of █ characters at row 2 and a row of ▀ at row 20. Lines 50–70 draw vertical bars on the left edge (column 0), the center divider (column 15), and the right edge (column 31) using ▌ and ▐ characters. This gives the appearance of a clean box without any DRAW commands.

Lines 85–100 pre-fill each data row (rows 5–19) with 14 underscores in the Side A column and 15 underscores in the Side B column. These serve as visual baselines for entries.

OVER 1 Printing

Data entry output uses OVER 1 (line 178, 190, 245, 270), which XORs printed pixels with the existing screen content. This allows program titles to overwrite the underscore baseline without completely erasing it, though in practice the underscore characters are fully replaced by the text characters due to pixel overlap. This is a common label-formatting trick on the Spectrum.

STOP Key Detection

Lines 170 and 240 check whether the user entered " STOP " (a padded string). When SYMBOL SHIFT + A is pressed at an INPUT prompt, the Spectrum inserts the keyword STOP followed by spaces to fill the input buffer representation. The program uses this as a signal to skip to the next section rather than exiting with an error, which is a well-known idiom for graceful early exit from INPUT loops.

Confirmation / Redo Mechanic

After each entry, lines 192 and 272 ask “OK (ENT/N)”. If the user types N or n, the program re-prints the previous values using uppercase variable names (N$, I$) over the same screen positions before looping back to re-enter that row. Note that lowercase n$ and i$ are used for new input, while uppercase N$ and I$ implicitly refer to the same variables in Spectrum BASIC (variable names are case-insensitive for non-string variables, but string variable names are case-sensitive — see anomaly below).

Bugs and Anomalies

• Case-sensitive string variable name mismatch: The program stores input in n$ and i$ (lowercase), but the redo branch at line 192 reprints N$ and I$ (uppercase). In Spectrum BASIC, n$ and N$ are distinct variables, so the redo display would show whatever was previously stored in the uppercase versions (initially empty strings), not the most recently entered values. This is a genuine bug likely introduced during transcription of the incomplete listing.
• DIM N$(10) unused: Line 30 dimensions an array N$(10), but the program never uses it — all title data is stored in the simple string variable n$. This array declaration is dead code, possibly a remnant from an earlier version of the program.
• No actual LPRINT/COPY output: Despite the setup message instructing the user to turn on the printer, the program contains no LPRINT, LLIST, or COPY command. The label is drawn to the screen only. The POKE to 23609 (printer line spacing) is therefore also inert for the program’s actual operation.
• STOP at line 310: The program ends with a STOP statement rather than returning to a menu or offering a reprint option.

Key Variables

Variable	Purpose
a$	Tape title, printed at row 1
n$ / N$	Current program title entry (case mismatch bug)
i$ / I$	Current index number entry (case mismatch bug)
o	Entry counter displayed in prompts (1–15)
n	Loop variable for screen row (5–19)
Z$	General input holder for ENTER/confirmation prompts