Geography Quiz

This program displays a color-filled map of North America and then runs a geography quiz asking the user to name U.S. state capitals. The map is built using two techniques: attribute-cell color fills via POKE to the display file starting at address 22528, and a pixel-precise outline drawn with chained PLOT/DRAW commands. Canada and Mexico are rendered in white (PAPER attribute 56), while the United States is rendered in a separate pass using attribute value 32 (green on blue). Country and region labels are printed with PAPER and INK color changes using AT coordinates. The quiz section reads state/capital pairs from DATA statements, accepts INPUT from the user, and compares the response string directly against the stored answer.

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Program Analysis

Program Structure

The program is divided into several logical phases controlled by sequential GO TO and GO SUB jumps:

1. Lines 10–13: Introduction/dedication message, then CLS.
2. Lines 100–390: Set cyan paper background, draw the USA shape by POKEing attribute cells, then STOP (never reached due to GO TO 500 at line 220 when sentinel is hit).
3. Lines 500–700: Draw Canada and Mexico by POKEing white attribute cells.
4. Lines 800–960: Add country/region name labels with colored PAPER/INK, then call subroutine 2000.
5. Lines 1000–1060: Border-drawing subroutine using PLOT/DRAW.
6. Lines 2000–3030: Pixel-level outline subroutine drawing the continental USA silhouette via chained DRAW segments.
7. Lines 4000–4200: Geography quiz loop — reads state/capital pairs, accepts user input, compares, and reports.
8. Lines 4250: DATA for the quiz (five state/capital pairs).
9. Lines 9995–9999: STOP, SAVE, and VERIFY.

Map Rendering via Attribute POKEs

The filled country regions are created by writing directly to the color attribute file, which begins at address 22528. Each cell corresponds to one 8×8 character position. The formula used is:

P = 22528 + (R * 32) + S

where R is the screen row and S is the starting column. A loop then POKEs L consecutive cells with the chosen attribute byte. The USA uses attribute value 32 (green ink, black paper in standard palette) and Canada/Mexico use 56 (white ink, black paper). This approach fills rectangular runs of cells efficiently without touching the pixel bitmap, so the background color changes appear immediately without any drawing overhead.

DATA Format for Map Fills

Each country’s fill data is a sequence of triplets R, S, L — row, start column, and length — terminated by the sentinel 100, 100, 100. The same READ/sentinel loop pattern is used twice (lines 210–280 for the USA, lines 510–570 for Canada/Mexico), making the structure consistent and easy to extend. Note that line 365 contains the triplet 19,0,1,0,0,3, which is actually two triplets concatenated on one line: 19,0,1 and 0,0,3 — the latter POKEs row 0, column 1 through 3, adding a small fill at the very top of the screen.

Pixel Outline Subroutine (Lines 2000–3030)

Subroutine 2000 draws a detailed pixel-level silhouette of the continental USA coastline using a long sequence of horizontal and vertical DRAW commands (all movements are multiples of 8 pixels, aligning to character cell boundaries). The outline starts at pixel coordinate (48, 128) and proceeds clockwise around the map shape. A PAUSE 100 at line 3025 gives a brief pause before returning, letting the user see the completed outline. INK 0 is set at line 2005 so the outline is drawn in black over the colored attribute cells.

Border Subroutine (Lines 1000–1060)

The screen border is drawn by subroutine 1000 using four DRAW calls from a starting PLOT 0,0 at the bottom-left corner, tracing a rectangle 255 pixels wide and 175 pixels tall — covering nearly the full 256×176 pixel display area.

Geography Quiz Logic

The quiz at line 4000 uses a simple READ/INPUT/IF loop. It reads a state name into A$ and its capital into B$, prompts the user, compares C$ (user input) directly against B$ as a string, and prints feedback. A correct answer loops back via GO TO 4030; an incorrect answer also returns to 4030 after displaying the right answer. When all DATA is exhausted, BASIC will generate an error — there is no explicit end-of-data sentinel, so the quiz terminates with an “Out of DATA” error rather than a graceful message.

Notable Techniques and Idioms

• The blank string L$=" " (32 spaces) at line 4040 is used to erase previously printed lines by overwriting them, a standard screen-clearing trick for partial rows.
• PAPER and INK statements are used inline before PRINT to change colors for individual labels without needing separate attribute POKEs.
• The map-drawing data is split across multiple DATA lines (300–370 for USA, 605–700 for Canada/Mexico) but both data sets are read sequentially from the same data pointer, relying on BASIC’s single shared READ pointer and the sentinel value to switch between regions.
• Line 390 contains a STOP that is never reached during normal execution (flow goes to line 500 via the sentinel branch at line 220), serving as a defensive measure.

Bugs and Anomalies

Location	Issue
Line 4250	Only five state/capital pairs are in the DATA. The quiz loop has no end-of-data guard, so it will crash with an error after exhausting all entries.
Line 4250	“BIRMINGHAM” is listed as the capital of Alabama; the actual capital is Montgomery. This is a factual error in the quiz data.
Line 4160	PRINT AT 21,0;L$ and PRINT AT 3,0;L$ attempt to clear rows 21 and 3 after showing the answer, but row 3 is also used at line 4100 for “YOUR ANSWER WAS:” — timing of these clears may cause visual glitches depending on PAUSE durations.
Lines 100–130	The comment says “sets map background color to cyan” but PAPER 1 is blue, not cyan (cyan is PAPER 5). The comment is incorrect.