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   ► KBTo/From GuidesPerlOperators  Print This     

Cross Ref > Operators

By Mike Prestwood

Perl versus Access VBA: A side by side comparison between Perl and Access VBA.


A language symbol used for assignment, comparison, computational, or as a logical.


[Other Languages] 

Languages Focus

Common assignment operators for languages include =, ==, and :=. An assignment operator allows you to assign a value to a variable. The value can be a literal value like "Mike" or 42 or the value stored in another variable or returned by a function.

Perl:   =

Perl assignment operators:

= Assignment $x = 8;
+= Addition $x += 8;
-= Substraction $x -= 8;
*= Muliplication $x *= 8;
/= Division $x /= 8;
%= Modulus $x %= 8;
**= Exponent $x **= 8;

Syntax Example:
$FullName = "Randy Spitz";
$Age = 38;
Access VBA:   =

Access uses = for it's assignment operator.

Syntax Example:
Dim Age As Integer
Dim FullName As String
FullName = "Randy Spitz"
Age = 38

Comparison Operators

[Other Languages] 

General Info: Round Floating Point Numbers

When comparing floating point numbers, make sure you round to an acceptable level of rounding for the type of application you are using.

Languages Focus

A comparison operator compares two values either literals as in "Hello" and 3 or variables as in X and Counter. Most languages use the same operators for comparing both numbers and strings. Perl, for example, uses separate sets of comparison operators for numbers and strings.

Perl:   ==, !=

Common comparison operators:

== equal
!= not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Perl also offers additional string comparison operators:

eq string equals
ne string not equal
lt string less than
gt string greater than
le string less than or equal
ge string greater than or equal

Syntax Example:
#Does Perl evaluate the math correctly? No!
if ((.1 + .1 + .1) == .3) {
} else {
print("Not correct<br>");
Access VBA:   =, <>

Save as VB Classic. Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Syntax Example:
//Does Access evaluate the math correctly? No!
If 0.1 + 0.1 + 0.1 = 0.3 Then
MsgBox "correct"
MsgBox "not correct"
End If

Empty String Check

[Other Languages] 

Languages Focus

An empty string is a zero length string, a string that is equal to null (""), or not assigned. In some languages, you can check if a string is empty by comparing it to an empty string (""). Some languages distinguish between nil and null ("") so checking if the length is 0 is easier.

[Not specified yet. Coming...]
Access VBA:   Len(s&vbNullString)

In Access VBA, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Syntax Example:

All these will work for variables unassigned, set to "", or set to Null:

If s&"" = "" Then
  MsgBox ("Quotes with &'' say null is empty")
End If
If Len(s&"") = 0 Then
  MsgBox ("Len with &'' says null is empty")
End If
If Len(s&vbNullString) = 0 Then
  MsgBox ("Using vbNullString also works!")
End If

Logical Operators

[Other Languages] 

Languages Focus

Logical operators perform conditional and, or, and not operations. Some languages support both binary logical operators that link two and unary logical operators negate (make opposite) the truth value of its argument. Finally, some languages short circuit logic. For example, with this or that, if this is an expression returning true, then that is never executed.


Perl logical operators:

&& or and and, as in this and that
|| or or or, as in this or that
! Not, as in Not This

Syntax Example:
#Given expressions a, b, c, and d:
if !((a && b) && (c || d)) {
  #Do something.
Access VBA:   and, or, not

Same as VB. Access VBA logical operators:

and and, as in this and that
or or, as in this or that
Not Not, as in Not This

Access VBA never short circuits. Given the expression this or that as well as this and that, if this evaluates to false, then that is still executed.

Syntax Example:
'Given expressions a, b, c, and d:
If Not (a and b) and (c or d) Then
  'Do something.
End If

String Concatenation

[Other Languages] 
Perl:  "String Concatenation" .

Perl uses a period (.) known as a dot to concatenate strings.

Syntax Example:
$fname = "Mike";
$lname = "Prestwood";

$fullname = $fname . $lname . "

print "My name is " . "Mike.
Access VBA:  "String Concatenation" & or +

Although you can use either a & or a + to concatenate values, my preference is to use a + because more languages use it. However, if you use & then some type conversions are done for you. If you use + you will sometimes have to cast a value to concatenate it. For example, you will have to use CStr to cast a number to a string if you use the + operator as a concatenation operator.

Syntax Example:
Dim FirstName As String
Dim LastName As String
FirstName = "Mike"
LastName = "Prestwood"
MsgBox "Full name: " & FirstName & " " & LastName
MsgBox "2+2=" + CStr(2+2)

Unary Operators

[Other Languages] 

General Info: Unary Operator

An operation with only one operand (a single input). Common unary operators include + plus, - minus, and bitwise not. Some operators can function as both unary and binary operators. For example, + and - operators can serve as either.

Languages Focus

What unary operators are supported in additoin to the standard plus, minus, and bitwise not.


An operation with only one operand (a single input). The following are the Perl unary operators: !, -, ~, +, \, &, and *.

  • ! performs logical negation which is "not"
  • - performs arithmetic negation if the operand is numeric.
  • ~ performs bitwise negation, that is 1's complement.
  • + has no semantic effect whatsoever, even on strings.
  • \ creates a reference to whatsoever follows.
  • & Address of operator.
  • * Dereference address operator.
Access VBA: 

An operation with only one operand (a single input) such as +, -, and Not.

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