Commodore Plus 4 - Page 184

SOOA
200D
200P
SOU
2012
2014
2016
2018
2019
201C
9D
C9
FO
E8
EO
90
BO
E8
8E
00
9F 05
OD
07
48
Fl
01
66 05
STA
CMP
BEQ
IWX
CPX
BCC
BCS
INX
STX
BRK
$059F,X
#$0D
$2018
#$48
$2007
$2019
$0566
Store in the HELP key's definition
area.
Look for a carriage return.
When found, quit.
Increment the pointer.
Compare to the maximum allowed.
If not there yet, go on.
If there, quit.
Increment the pointer to get a count
Store count in HELP key length.
Stop processing.
Note: There is an "unofficial" ROM subroutine that redefines a function key.
Store the key to redefine (0 to 7) in $76, the address of the new definition is
$22-$23, load .A with the length of the definition and call the subroutine at
$FF49.
Mathematical Calcinations
This section briefly discusses a few important concepts for using your computer
for calculating.
Number Storage In BASIC there are two numeric variable types. The more
straightforward is the integer variable (signified by attaching a % to the variable
name). An integer variable can have values from -32767 to +32767. Theoretically,
a value of -32768 is allowed. Try the following example program:
10 N%=32768
20 PRIETT
The result will be a -32768. So much for theory.
The second variable type is floating point. The format of floating point number
storage is examined in the section on USR in Chapter 5. The largest magnitude of
a floating point number is 1.70141183E+38, and the smallest magnitude distin
guishable from zero is 2.93873588E-39. The floating point format allows about
nine decimal digits of accuracy.
Speeding Up Calculations The first rule to speed calculations is to do as few as
possible. In particular, unless variable space is at a premium, do not calculate the
same quantity twice. Calculate it once, and save the value in a variable. The
exponentiation function (up arrow) is slow, so avoid it if possible. In particular,