Basic BASIC

This collection of introductory BASIC programs teaches fundamental programming concepts through character graphics, covering INPUT/OUTPUT, PRINT AT positioning, FOR/NEXT loops, GOSUB/RETURN subroutines, INKEY$ polling, and simple collision detection. Each mini-program draws block-graphic figures — a stick person, a juggler, a penguin, a car, and a traffic officer — using the block graphic character set to create crude but recognizable shapes. The juggler program demonstrates a simple real-time game loop where the player presses “M” to move a ball upward to catch a falling star, with collision detection at a specific screen coordinate. Several programs use the PRINT AT statement to confine user prompts to line 21, keeping the play area clear while awaiting INPUT. Variable pairs D (down/row) and A (across/column) are used consistently across programs as a movable anchor point for multi-row sprite drawing.

Program Analysis

This listing is a compilation of several independent short programs, each demonstrating a specific BASIC concept. They appear to be teaching exercises from a structured course, progressing from simple INPUT/PRINT through subroutines and real-time INKEY$ polling. The programs are not linked to each other; each starts at line 10 (or nearby) and stands alone.

Program Structure Overview

Sprite Representation

All figures are drawn as 3-row tall character sprites using block graphics and standard ASCII characters. The consistent convention uses variable D for the row and A for the column, with PRINT AT D,A, PRINT AT D+1,A, and PRINT AT D+2,A forming each sprite. This pattern appears in every program in the collection and is clearly the central pedagogical technique being taught.

Erase routines (e.g., lines 250–290 in the Cartoon Show and Penguin programs) simply reprint three spaces at the same coordinates, overwriting the sprite — a straightforward but effective approach without needing CLS.

Juggler Game

The juggler game is the most technically complex segment. It maintains two moving objects: a star that increments column A across row 7, and a ball at column 22 whose row D decreases when the player holds “M”. Key logic:

• Line 60 prints a star character at AT 7,A; line 70 erases the previous ball position with "." before redrawing at line 90 — a simple erase-before-draw animation technique.
• Collision is checked at line 100: IF D=7 AND A=21 THEN GOTO 300, requiring precise positioning.
• Line 110 resets the ball to row 18 if it reaches row 6, preventing it going off-screen.
• Line 120 wraps the star back to column 0 when it reaches column 30.
• The GOSUB at line 20 draws the juggler figure once at the start; the figure is not redrawn each loop, relying on the display not being cleared.

INKEY$ Usage

Two different INKEY$ patterns are demonstrated. In lines 220–240 of the first segment, a polling loop toggles display text based on whether any key is pressed, using two consecutive IF INKEY$ = "" and IF INKEY$ <> "" checks — note that between the two checks the key state could change, making these not truly atomic. In the juggler and movement demos, INKEY$ is polled inline within the game loop to steer objects, which is the more typical real-time usage.

Movement Demo Structure

The movement demo places four independent motion routines at different line-number bands (10–50, 90–130, 190–240, 290–350), each ending with STOP so only the currently RUN segment executes. The “move up” section at lines 290–350 uses a INKEY$-driven loop rather than FOR/NEXT, polling for “M” to decrement D and looping back with GOTO 310, which means the figure only moves when the key is held and stops otherwise — a non-trivial behavioral difference from the FOR/NEXT examples.

Notable Idioms and Techniques

• Prompts are printed using PRINT AT 21,0 with trailing spaces to overwrite previous longer prompts, keeping the display area clean without CLS.
• The cartoon show uses a FOR J=1 TO 80 loop alternating two GOSUB sprite routines to create a simple two-frame animation cycle.
• Quoted strings containing a literal double-quote use the doubled-quote escape, e.g., "SANDY""S" and "DON""T TOUCH".
• REM lines are used liberally as inline documentation, consistent with the teaching purpose of the listing.
• The copyright notice embedded in a REM at line 270 uses inverse-video block characters to spell out a company name, which is invisible to the running program but visible in the listing.

Potential Issues

• In the juggler game, line 70 uses PRINT AT D,22;"." to erase the ball by printing a period rather than a space — this leaves a dot artifact at every previous ball position rather than truly erasing it.
• The double INKEY$ check at lines 220–230 (first segment) reads the keyboard twice in sequence; rapid or borderline keypresses could produce inconsistent results since both branches might fire or neither might fire.
• In the “move up” section (lines 300–350), the initial LET D=20 at line 300 is outside the loop, so after CLS and GOTO 300 at lines 340–350, D is correctly reset each cycle — this is intentional design.
• Sandy’s Cartoon Show has a line 20 REM GET VALUE FOR D that immediately precedes a PRINT AT 21,0 prompt, but line 100 calls GOSUB 200 and line 110 calls GOSUB 300 in the same loop iteration with no erase between them, so the two sprite variants are drawn on top of each other each frame rather than alternating cleanly.

   3 REM USING INPUT
   5 REM GET VALUE FOR D
  10 PRINT "HOW FAR DOWN?"
  20 INPUT D
  25 REM GET VALUE FOR A
  30 PRINT "HOW FAR ACROSS?"
  40 INPUT A
  45 REM DRAW PERSON AT D,A
  50 PRINT AT D,A;" O▗"
  60 PRINT AT D+1,A;"▛[:]▀"
  70 PRINT AT D+2,A;"▗█▖"
  80 STOP
 100 REM DOING IT OVER AND OVER
 110 PRINT AT 21,0;"HOW FAR DOWN?  "
 120 INPUT D
 130 PRINT AT 21,0;"HOW FAR ACROSS?"
 140 INPUT A
 150 PRINT AT D,A;" O▗"
 160 PRINT AT D+1,A;"▛[:]▀"
 170 PRINT AT D+2,A;"▗█▖"
 180 GOTO 110
 200 REM FUNNY LITTLE PROGRAM
 210 REM USE  INKEY$
 220 IF INKEY$ ="" THEN PRINT AT 10,10;"               "
 230 IF INKEY$ <>"" THEN PRINT AT 10,10;"DON""T TOUCH"
 240 GOTO 220
 
  10 PRINT "PRESS M TO CATCH STAR"
  20 GOSUB 200
  25 REM STAR STARTS AT 0
  30 LET A=0
  35 REM BALL STARTS AT 18
  40 LET D=18
  45 REM LOOP TO MOVE BOTH
  50 LET A=A+1
  55 REM MOVE STAR
  60 PRINT AT 7,A;".*"
  70 PRINT AT D,22;"."
  80 IF INKEY$ ="M" THEN LET D=D-1
  85 REM DRAW BALL
  90 PRINT AT D,22;"O"
  95 REM CHECK FOR COLLISION
 100 IF D=7 AND A=21 THEN GOTO 300
 110 IF D=6 THEN LET D=18
 120 IF A=30 THEN LET A=0
 130 GOTO 50
 200 REM DRAW JUGGLER
 210 PRINT AT 19,20;" O▐"
 220 PRINT AT 20,20;"▛[:]▀"
 230 PRINT AT 21,20;"▗█▖"
 240 RETURN
 300 REM GOT ONE,SO START OVER
 310 PRINT AT 21,0;"[G][O][T]█[O][N][E]"
 320 PAUSE 100
 330 CLS
 340 GOTO 10
 
  10 PRINT "SANDY""S CARTOON SHOW"
  20 REM GET VALUE FOR D
  30 PRINT AT 21,0;"HOW FAR DOWN? "
  40 INPUT D
  50 REM GET VALUE FOR A
  60 PRINT AT 21,0;"HOW FAR ACROSS?"
  70 INPUT A
  80 PRINT AT 21,0;"HI THERE       "
  90 FOR J=1 TO 80
 100 GOSUB 200
 110 GOSUB 300
 120 NEXT J
 130 PRINT AT 21,0;"ERASE IT?(Y/N)"
 140 INPUT E$
 150 IF E$="Y" THEN GOSUB 250
 160 GOTO 20
 200 REM DRAW PERSON AT D,A
 210 PRINT AT D,A;" 0"
 220 PRINT AT D+1,A;"▀█▀"
 230 PRINT AT D+2,A;"▀▜ "
 240 RETURN
 250 REM ERASE FIGURE AT D,A
 260 PRINT AT D,A;"   "
 270 PRINT AT D+1,A;"   "
 280 PRINT AT D+2,A;"   "
 290 RETURN
 300 REM DRAW PERSON 2
 310 PRINT AT D,A;" 0"
 320 PRINT AT D+1,A;"▀█▀"
 330 PRINT AT D+2,A;" ▛▀"
 340 RETURN
 
  10 REM MOVE RIGHT
  20 FOR A=0 TO 25
  30 PRINT AT 10,A;" ▙"
  40 NEXT A
  50 STOP
  90 REM MOVE LEFT
 100 FOR A=25 TO 0 STEP -1
 110 PRINT AT 10,A;"█ "
 120 NEXT A
 130 STOP
 190 REM MOVE DOWN
 200 FOR D=0 TO 20
 210 PRINT AT D,15;" "
 220 PRINT AT D+1,15;"[*]"
 230 NEXT D
 240 STOP
 290 REM MOVE UP
 300 LET D=20
 310 IF INKEY$ ="M" THEN LET D=D-1
 320 PRINT AT D,17;"█"
 330 IF D<>0 THEN GOTO 310
 340 CLS
 350 GOTO 300
 
   5 REM PRINT GREETING
  10 PRINT "HELLO"
  20 PRINT "FROM"
  30 PRINT "SANDY"
  40 STOP
  42 REM 
  45 REM PRINT BOX
  50 PRINT "▛▀▜"
  60 PRINT "▌ ▐"
  70 PRINT "▙▄▟"
  80 STOP
  90 REM 
 100 REM USE   PRINT AT  TO DRAW     IN THE MIDDLE OF THE SCREEN
 105 REM 
 110 REM DRAW CAR
 120 PRINT AT 10,7;"▗▄ "
 130 PRINT AT 11,7;"█[-]█"
 140 PRINT AT 12,7;"O O"
 145 REM 
 150 REM DRAW TRAFFIC OFFICER
 160 PRINT AT 10,12;" O▐"
 170 PRINT AT 11,12;"▀[:]▀"
 180 PRINT AT 12,12;"▗█▖"
 190 STOP
 200 REM USE  LET  TO MAKE A         DRAWING EASY TO MOVE
 210 LET D=18
 220 LET A=25
 230 PRINT AT D,A;"▗▄ "
 240 PRINT AT D+1,A;"█[-]█"
 250 PRINT AT D+2,A;"O O"
 260 STOP
 270 REM [C][O][P][R]1983[2][-][B][I][T]█[S][O][F][T][W][A][R][E]
 
  10 PRINT "I WILL DRAW A PENGUIN"
  20 PRINT "WHERE YOU TELL ME TO"
  30 REM USING INPUT
  40 REM GET VALUE FOR D
  50 PRINT AT 21,0;"HOW FAR DOWN?  "
  60 INPUT D
  70 REM GET VALUE FOR A
  80 PRINT AT 21,0;"HOW FAR ACROSS?"
  90 INPUT A
 100 REM DRAW PERSON AT D,A
 110 GOSUB 200
 140 PRINT AT 21,0;"ERASE IT? (Y/N)"
 150 INPUT E$
 160 IF E$="Y" THEN GOSUB 250
 170 GOTO 50
 200 REM DRAW PENGUIN AT D,A
 210 PRINT AT D,A;">[.]▌"
 220 PRINT AT D+1,A;" ▌▌"
 230 PRINT AT D+2,A;"▗▙▌"
 240 RETURN
 250 REM ERASE AT D,A
 260 PRINT AT D,A;"   "
 270 PRINT AT D+1,A;"   "
 280 PRINT AT D+2,A;"   "
 290 RETURN