Commodore PET User Manual page 397

Program 11, BOTTOM UP.
5 REM PROGRAM 11 BOTTOM UP
10 REM
~*
**
B LAN K E T __
**_**
20 REM CONTINUOUS-LINE DISPLAY OF ONE
30 REM CHARACTER ENTERED FROM THE
40 REM KEYBOARD
50 REM
****_*********************~*.*~
90 PRINT"HIT A KE'r' OR <R:> TO ENI.".;
100 GET CS:IF C$= .... GOTO 100
105 PR 1tH":']" . ; : REl'l CLEAR SCREEN
110 IF C$=CHR$(13) GOTO 170
115 F'RI t-./T "~~.na~~IQI •••••••••••••••••••• I"
117 F'OKE 33767,(ASC(C$)ANS128)/2 OR (ASC(C$)AND 63)
120 FOR 1=1 TO 999 :REM 999/40=25 LINE8
13~1
F'R 1NT C$.;
"1.'" . ;
140 NE;'(T
150 POKE 33767,(ASC(CS)AND128)/2 OR (ASC(C$)AND63)
160 GOTO 10(1
17(1 END
Changes
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Lines 5. 115, 117
Lines 120. 130, 160
Line 150
Lines 105 and 110
Comments
To print in reverse order, the program first needs to display the character at
the last screen position (Iower right-hand corner). We saw in Program 10 that this
could be done only by POKEing the screen character equivalent of the C$
character code; the mechanics were ail worked out in Program 10. In the current
program. line 117 is an exact duplicate of the Program 10 POKE line; it displays
the C$ character at the last screen position.
The next task is to print the character at the next-to-Iast position. At line 115
the cursor is moved from its home position to position 1 of the last line by 24 cur-
sor downs and then over to the next-to-Iast position by 38 cursor rights. After
POKEing the last character (Iine 117), the program begins printing C$ to the other
999 positions of the screen. After each PRINT (Iine 130) the cursor rests at the
position following the position where the last character was printed.
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