Decoration of Independence

This program displays an American Independence Day tribute, cycling through the original 13 colonies in the order they ratified the Constitution before rendering a graphic of the 13-colony flag. For each colony, an animated firework effect is produced using block graphics characters (CHR$ 133 and 128) that scroll upward from the bottom of the screen, with a starburst shape drawn at the top using block graphics CHR$ 134 and 137. The flag rendering uses the ZX Spectrum’s block graphics characters: CHR$ 143 (solid block, red ink) for stripes, CHR$ 128 (quarter block, green ink) for alternate stripes, and a canton drawn with solid block graphics and inverse-mode asterisks arranged in a circular star pattern. The program loops back to the colony display on a “Y” keypress, using a string dimension array C$(13,20) to store the colony names.

---

Program Analysis

Program Structure

The program is organized into three main phases: an introduction, a colony fireworks loop, and a flag display. Line numbers begin at 5001 and run to 9998, suggesting this was part of a larger program or type-in listing with deliberate spacing. The flow is essentially linear with a replay loop at the end.

1. Introduction (5001–5018): Title screen with border/ink/paper setup, a short beep, and an explanatory message with a 500-frame pause.
2. Initialization (5020–5260): Arrays are dimensioned and filled with block-graphic characters for later use as stripe rows.
3. Colony fireworks loop (5270–5350): Iterates through all 13 colonies, displaying the colony name and an animated firework.
4. Flag display (5360–5465): Renders the 13-colony flag using stripe arrays and inverse asterisks for the star canton.
5. Replay prompt (5470–5482): Asks the user to play again, looping back to line 5260 on “Y”.

Array Usage

Variable	Size	Purpose
C$(13,20)	13 strings × 20 chars	Colony names in ratification order
B$(30)	30 chars	One row of red solid block graphics (CHR$ 143) for flag stripes
G$(30)	30 chars	One row of green quarter-block graphics (CHR$ 128) for alternate stripes
S$(12)	12 chars	One row of blue solid block graphics (CHR$ 143) for the canton rows

Firework Animation

The firework effect (lines 5290–5340) picks a random horizontal position R between 5 and 25 using LET R=RND*20+5. A rising spark is simulated by printing CHR$ 133 (a half-block) at each row from 19 down to 5, immediately overwriting it with a space to create motion. At the apex, a starburst is constructed using four block-graphic characters around the center:

• CHR$ 128 — center top (solid quarter block)
• CHR$ 134 — upper-left and lower-right diagonal branches
• CHR$ 137 — upper-right and lower-left diagonal branches

The screen is then cleared with CLS before the next colony, so the starburst is only briefly visible — there is no deliberate pause after the burst, making the effect quite fast.

Flag Rendering

The 13 stripes are produced by alternating B$ (red, CHR$ 143 × 30) and G$ (green ink, CHR$ 128 × 30) six times with an extra B$ row, giving 13 stripe rows total (lines 5370–5410). The canton (blue field) is overlaid at rows 5–11 by printing the 12-character S$ seven times in ink 1 (blue) starting at column 0 (lines 5430–5450). Two additional solid-block characters are stamped at positions to reinforce the canton corners using the escape \::\:: (four solid block chars).

The 13 stars are drawn using INVERSE 1 and asterisk characters arranged in a circular/oval pattern across lines 5–10, columns 3–9, mimicking the Betsy Ross flag’s ring of stars (line 5460).

Notable Techniques

• Pre-filling string arrays B$, G$, and S$ with repeated block-graphic characters at initialization avoids re-computing them in the display loop.
• The INK attribute is set before assigning characters to G$ at line 5210, but since string variables don’t store color attributes, this ink change only affects subsequent PRINT calls — the ink colors for flag stripes are set immediately before each PRINT B$ / PRINT G$ call.
• The replay loop uses a non-empty check: IF R$="" THEN GO TO 5480 (line 5480) before testing for “Y”, which guards against an empty INPUT response re-entering the condition check rather than the INPUT statement itself.

Bugs and Anomalies

• The INK 2 at line 5210 sets green ink for G$ character assignment, but since character attributes are not stored in string variables, the actual color of the alternate stripes depends on the prevailing ink at print time. The INK 2 at line 5365 correctly sets this before the stripe printing loop begins.
• C$(2) is set to "PENNSYLVANIA " with two trailing spaces — these are harmless padding since the array dimension is 20 characters, but they are unnecessary.
• The title at line 5275 reads “FIRST OF FIFTY” rather than referencing the 13 colonies, which is thematically inconsistent with the explanatory text on screen — this appears to be an artifact from the original magazine listing.
• The flag uses green ink (INK 2) for alternating stripes instead of white (INK 7), likely due to the limited color contrast between white stripes and the white paper background.
• Line 5000 is referenced in the SAVE "DECOR" LINE 5000 statement but does not exist in the listing; the program actually begins at line 5001. This means the auto-run target is a non-existent line, which on the Spectrum falls through to the first available line.