PowerBASIC Information Center Tutorials
These tutorials were written to help you get a quick, but thorough, understanding of PowerBASIC -
the scope of the language as well as it's specific capabilities.
PowerBASIC supports a pretty much standard set of operators.
Some languages have operators specific to string or number types,
but PowerBASIC operators work on both types. Here's a
compact listing of the operators PowerBASIC supports. This tutorial breaks
these into common groups for discussion.
Note that operators can be made of letters (such as MOD) and do not always
consist of special characters.
+ += < AND AND=
- -= > OR OR=
* *= <> NOT NOT=
/ /= >< XOR XOR=
\ \= <= EQV EQV=
MOD MOD= =< IMP IMP=
The following, industry-standard operators are used to perform basic arithmetic
= x = 2 # assignment
+ x = x + 1 # add
- x = x - 1 # subtract
* x = x * 2 # multiply
/ x = x / 2 # divide
\ x = x \ 2 # integer division
^ x = x^2 # raises x to the power of 2
MOD x MOD 5 # modulus (whole number remainder of division)
MOD is an example of an operator that is defined using letters
rather than special characters.
These operators compare two values or expressions. They return
a Boolean result of TRUE (-1) or FALSE (0). Since they return
a numeric result, they can be use in numerical expressions to
return a -1 or 0. However, relational operators are most notably
used in flow control structures, such as IF, DO, WHILE, etc., which
use the TRUE/FALSE value of an expression to determine which source
code statements to execute.
< # less than
> # greater than
<> or >< # not equal to
<= or =< # less than or equal to
>= or => # great than or equal to
When used with strings, the ASCII values of each character in the
string form the basis for the comparison. For example, "a" is less
than "A" because their respective ASCII codes are 39 and 65.
The PowerBASIC uses two operators (+ and &) to join strings.
b$ = "dog" 'assign "dog" to string variable a$
c$ = "cat" 'assign "cat" to string variable c$
a$ = b$ + c$ 'a$ = "catdog"
a$ = b$ & c$ 'a$ = "catdog"
This is a comparative slow process and programmers are
advised to use the special BUILD$ function which concatenates
strings with much greater speed, particularly with larger numbers
of strings to concatenate.
Boolean Values and PowerBASIC Functions
Before getting into PowerBASIC Boolean operators, here are some
points to remember when dealing with Boolean values and
- In PowerBASIC, numeric zero or an empty string are treated as FALSE.
All other values are considered TRUE.
- PowerBASIC functions which return a Boolean result return -1 to
indicate TRUE and 0 to indicate FALSE.
- Some PowerBASIC operators evaluate expressions in terms of their
TRUE/FALSE value and some act on the numeric/string value of the
These PowerBASIC operators can be used in two ways - to compare
the TRUE/FALSE value of two expressions, or to manipulate the
content of a variable at the bit level. All but the NOT
operator work on two expressions.
and # TRUE if both expressions TRUE
or # TRUE if either expression TRUE
xor # TRUE if arguments have different Boolean values
not # returns bitwise one's-complement of a single argument
eqv # TRUE if arguments have same Boolean values
imp # FALSE only if 1st argument is T and 2nd argument is F
From a Boolean viewpoint, when dealing with values 0 and -1, NOT works as
expected. But when NOT is used on other values, it can provide unexpected
results. This is because NOT works at the bit level, not on a Boolean level.
In cases where the expression to be evaluated is other than 0 or -1, the
ISFALSE and ISTRUE operators should be used to deal with values on a Boolean level.
Bit Manipulations by Boolean Operators
All of the Boolean operators above operate at the bit level. The section
above shows how the operators can successfully be used to perform
Boolean tests. Here is a description of the bit-level effect of the
operators. You can see how the AND/OR and NOT/XOR pairs provide
effects opposite to one another.
AND sets selected bits to 0 without affecting the other bits
OR sets selected bits to 1 without affecting the other bits
NOT reverses all bits
XOR reverses selected bits
The EQV and IMP also perform bit-level manipulation but the results
are seldom used for that purpose. The Boolean descriptions of the prior
section describe the effects most useful to programmers.
To simplify coding, PowerBASIC also offer the ability to combine the
following operator pairs for common operations. The operator, its
use, and the equivalent expressions are given in the following table.
+= x+=5 x = x+5
-= x-=5 x = x-5
*= x*=5 x = x*5
/= x/=5 x = x/5
\= x/=5 x = x\5
MOD= x%=5 x = x%5
AND= x AND= 6 x = x AND 6
OR= x OR= 5 x = x OR 5
XOR= x XOR= 3 x = x XOR 3
EVQ= x EQV= 6 x = x EQV 6
IMP= x IMP= 2 x = x IMP 2
+= x += "dog" x = x + "dog"
&= x &= "dog" x = x & "dog"
All of these compound operators are described as replacing
a variable with its value modified (according to the operator type)
by a second value.
Other languages, such as Perl, provide the ability to insert variables
into quotes and at execution, substitute the variable value for the variable
name. The method is a shortcut for concatenating strings and variable values.
This is called interpolation and is not supported by PowerBASIC.
If you have any suggestions or corrections, please let me know.