Commodore VIC-20 - Page 89

Chapter 3: Programming the VIC 20 Computer 75
Boolean operators operate on integer operands one binary digit at a
time. VIC BASIC stores all numbers in binary format, using two's comple-
ment notation to represent negative numbers. Therefore
we can illustrate an
AND operation as follows:
43 AND 137 = 9---------,
I L...I ----: 89
16
- 10001001
L--------2B
I6
-OOlOlOll
09
16
- 00001001
Here is an OR operation.
43 OR 137= 171 ---------,
I \...1 ---: 89
16
- 10001001
~-----"2BI6 - 00 10 lOll
AB
I6
-lOlOlOll
Here are two NOT operations.
NOT 43 = 212 ----------,
L..I ---_I 2B
I6
- 00101011
l l
D4
16
- 1l010100
NOT 137= 118----------.
IL.. ---_I 89
16
_ 10001001
l l
76
16
- 01l1O1l0
If operands are not integers, they are converted to integer form; the
Boolean operation
is performed, and the result is returned as a 0 or 1.
If a Boolean operator has relational operands, then the relational
operand is evaluated to
-lor 0 before the Boolean operation is performed.
Thus the operation
A= I ORC< 2
is equivalent to