# ATARI BASIC Learning by Using by Thomas C. Rowley By Thomas C. Rowley

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In program mode the CHR\$ function can be used (ie. ) Suggestions: 1. Change line 45 45 PRINT" ";CHR\$(l59);" ";CHR\$(l59) 2. The tabs are normally set 10 spaces apart. This can be changed with a POKE to address 201. Try this. a) Press SYSTEM RESET b) Press the TAB key several times and note the movement. c) Type POKE 201,18 d) Press the TAB key several times again and note the movement of the cursor. 3. Write a program that prints random numbers in 3 columns tabbed at positions 15, 30 and 35 . Key Control This subroutine is used to convert all key entries to upper-case normal video.

Try some negative values as well. 3. Make this program work in another graphics mode. 4. Plot different algebra equations such as those for a hyperbola, circle or parabola. 1. 51 6 PEEKS, POKES and Special Stuff PEEK and POKE let you unleash a power not available through other BASIC commands. With these two key words, it is possible to look directly into a memory address and change the content of many of the addresses. PEEK is used to "read" the contents of a memory address. POKE is used to "write" to an address.

Add some colors with these line changes. Press the trigger (red) button to get another color. 30 55 60 70 X=0 :C=0 IF PTRIG(0) =0 THEN C=C+l COLOR C+l :PLOT X,10 COLOR C:PLOT Xl,10 4. Try this program in 2 dimensions by adding another paddle for vertical movement. 24 Joystick Drawing Use the joystick to draw on the screen. Here is a diagram ofthe values the computer returns to STICK(O). 5 Values of STICK(O) 14 )-------7 11--------------; 5 9 13 10 REM JOYSTICK DRAWING 50 REM SET UP SCREEN 60 GRAPHICS 3+16 70 X=19:Y=9 75 COLOR 1 80 PLOT X,Y 100 REM STICK POSITION 110 Z=STICK(0) 120 REM SCREEN POSITION 130 X=X+«Z=5)+(Z=7)+(Z=6)) 25 140 150 160 170 180 190 X=X-«Z=10)+(Z=11)+(Z=9» IF X<0 OR X>39 THEN X=39*(X>39) Y=Y-«Z=5)+(Z=9)+Z=13» Y=Y-«Z=6)+(Z=14)+(Z=10» IF Y<0 OR 7>23 THEN Y=23*(Y>23) · GOTO 80 The stick position is read in line 110.