Commodore VIC-20 - Page 88

74 The VIC 20 User Guide
IF X < Y OR B > = 44 THEN F = 0
F
is set to 0 if X is less than Y or B is greater than 43
IF A = 1 AND B = 2 OR C = 3 GOTO 30
Take the branch if both A = I and B = 2; also take
the branch if
C =3
A single operand can be tested for true or false. An operand appearing
alone has
an implied "< >0" following it. Any nonzero value is considered
true; a zero value
is considered false.
IF A THEN B= 2
IF A < > 0 THEN B = 2
The above two statements are equivalent
IF NOT B GOTO 100
Branch if B is false, i.e., equal to zero. This is
probably better written as
IFB= o GOTO 100
All Boolean operations use integer operands. If you perform Boolean
operations using floating point numbers, the numbers are automatically
converted to integers. Therefore, the floating point numbers must fall within
the allowed range
of integer numbers.
If you are a novice programmer, you are unlikely to use Boolean
operators in the manner that
we are about to describe. If you do not
understand the discussion, skip to the next section.
TABLE 3·3. Boolean Truth Table
The AND operation results in a 1 only if both numbers are 1
I
AND I = I
o AND 1 = 0
I ANDO= 0
o ANDO= 0
The OR operation results in a 1 if either number
is I
lOR 1 = 1
o OR 1 = 1
lOR 0 = 1
OORO= 0
The NOT operation logically complements each number
NOT 1 = 0
NOTO= 1