Microsoft Visual Basic for Applications Language Reference

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Microsoft Visual Basic for Applications Language Reference Page 1 of 1081
Microsoft Visual Basic for
Applications Language Reference
– Operator
Description
Used to find the difference between two numbers or to indicate the negative value of a numeric
expression.
Syntax 1
result = number1–number2
Syntax 2
–number
The – operator syntax has these parts
Part Description
result Required; any numeric variable.
number Required; any numeric expression.
number1 Required; any numeric expression.
number2 Required; any numeric expression.
Remarks
In Syntax 1, the – operator is the arithmetic subtraction operator used to find the difference
between two numbers. In Syntax 2, the – operator is used as the unary negation operator to
indicate the negative value of an expression.
The data type of result is usually the same as that of the most precise expression. The order of
precision, from least to most precise, is Byte, Integer, Long, Single, Double, Currency, and
Decimal. The following are exceptions to this order
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If Then result is
Subtraction involves a converted to a Double.
Single and a Long,
The data type of result is a converted to a Variant
Long, Single, or Date containing a Double.
variant that overflows its
legal range,
The data type of result is a converted to an Integer
Byte variant that overflows variant.
its legal range,
The data type of result is converted to a Long
an Integer variant that variant.
overflows its legal range,
Subtraction involves a Date a Date.
and any other data type,
Subtraction involves two a Double.
Date expressions,
One or both expressions are Null expressions, result is Null. If an expression is Empty, it is
treated as 0.
Note The order of precision used by addition and subtraction is not the same as the order of
precision used by multiplication.
See Also
Operator precedence.
Example
This example uses the – operator to calculate the difference between two numbers.
Dim MyResult
MyResult = 4 - 2 ' Returns 2.
MyResult = 459.35 - 334.90 ' Returns 124.45.
#Const Directive
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Description
Used to define conditional compiler constants for Visual Basic.
Syntax
#Const constname = expression
The #Const compiler directive syntax has these parts
Part Description
constname Required; Variant (String). Name of the
constant; follows standard variable naming
conventions.
expression Required. Literal, other conditional
compiler constant, or any combination that
includes any or all arithmetic or logical
operators except Is.
Remarks
Conditional compiler constants are always Private to the module in which they appear. It is not
possible to create Public compiler constants using the #Const directive. Public compiler
constants can only be created in the user interface.
Only conditional compiler constants and literals can be used in expression. Using a standard
constant defined with Const, or using a constant that is undefined, causes an error to occur.
Conversely, constants defined using the #Const keyword can only be used for conditional
compilation.
Conditional compiler constants are always evaluated at the module level, regardless of their
placement in code.
See Also
#If...Then...#Else directive, Const statement.
Specifics (Microsoft Access)
In Microsoft Access, you can define a public conditional compiler constant in the Declarations
section of a module. A public compiler constant is applicable to all modules in the current
database, but not in any other database.
You can also declare a public compiler constant by clicking Options on the Tools menu, then
clicking the Advanced tab. Enter the constant in the Conditional Compilation Arguments box.
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For example, you might enter the following expression into the Conditional Compilation
Arguments box.
conDebug = 1
You can use a public compiler constant in code in any module. For example, you can create an
#If...Then...#Else construct to optionally run debug code.
#If conDebug = 1 Then
. ' Run debug code.
.
.
#Else
. ' Run streamlined code.
.
.
#End If
To create multiple public conditional compilation constants, declare them on separate lines in
the Declaration section. In the Conditional Compilation Arguments box, separate them with
colons. For example, you can enter the following conditional compilation constants in the
Conditional Compilation Arguments box.
conActiveLanguage = 1 : conDebug = 1
You can use a logical operator to include both constants in an #If...Then...#Else construct. In
the following example, the first segment of code runs only if both constants are currently equal
to 1, so that the expression containing the constants is true.
#If (conActiveLanguage = 1 And conDebug = 1) Then
. ' Run debug code for the active language version.
.
.
#Else
. ' Run another code segment.
.
.
#End If
If either or both constants have a different value, then the code in the #Else portion of the
construct runs. To change which block of code runs, you can simply change the values of the
constants.
Notes
(cid:1) A conditional compilation constant is always evaluated with a text-based string
comparison method. This evaluation is equivalent to having an Option Compare Text
statement in the module and occurs even if the module contains an Option Compare
Database statement.
(cid:1) When writing code for conditional compilation, it may be less confusing to view one
procedure at a time rather than all procedures in the module. To change how you view
your code, click Options on the Tools menu, then click the Module tab. Under Code View,
clear the Full Module View check box.
Example
This example uses the #Const directive to declare conditional compiler constants for use in
#If...#Else...#End If constructs.
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#Const DebugVersion = 1 ' Will evaluate true in #If block.
#If...Then...#Else Directive
Description
Conditionally compiles selected blocks of Visual Basic code.
Syntax
#If expression Then
statements
[#ElseIf expression-n Then
[elseifstatements]]
[#Else
[elsestatements]]
#End If
The #If...Then...#Else directive syntax has these parts
Part Description
expression Required. Any expression, consisting
exclusively of one or more conditional
compiler constants, literals, and
operators, that evaluates to True or
False.
statements Required. Visual Basic program lines or
compiler directives that are evaluated if
the associated expression is True.
expression-n Optional. Any expression, consisting
exclusively of one or more conditional
compiler constants, literals, and
operators, that evaluates to True or
False.
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elseifstatements Optional. One or more program lines or
compiler directives that are evaluated if
expression-n is True.
elsestatements Optional. One or more program lines or
compiler directives that are evaluated if
no previous expression or expression-n
is True.
Remarks
The behavior of the #If...Then...#Else directive is the same as the If...Then...Else statement,
except that there is no single-line form of the #If, #Else, #ElseIf, and #End If directives; that is,
no other code can appear on the same line as any of the directives. Conditional compilation is
typically used to compile the same program for different platforms. It is also used to prevent
debugging code from appearing in an executable file. Code excluded during conditional
compilation is completely omitted from the final executable file, so it has no size or performance
effect.
Regardless of the outcome of any evaluation, all expressions are evaluated. Therefore, all
constants used in expressions must be defined — any undefined constant evaluates as Empty.
Note The Option Compare statement does not affect expressions in #If and #ElseIf statements.
Expressions in a conditional-compiler directive are always evaluated with Option Compare Text.
See Also
#Const directive, If...Then...Else statement.
Example
This example references conditional compiler constants in an #If...Then...#Else construct to
determine whether to compile certain statements.
' If Mac evaluates as true, do the statements following the #If.
#If Mac Then
'. Place exclusively Mac statements here.
'.
'.
' Otherwise, if it is a 32-bit Windows program, do this:
#ElseIf Win32 Then
'. Place exclusively 32-bit Windows statements here.
'.
'.
' Otherwise, if it is neither, do this:
#Else
'. Place other platform statements here.
'.
'.
#End If
& Operator
Description
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Used to force string concatenation of two expressions.
Syntax
result = expression1 & expression2
The & operator syntax has these parts
Part Description
result Required; any String or Variant variable.
expression1 Required; any expression.
expression2 Required; any expression.
Remarks
If an expression is not a string, it is converted to a String variant. The data type of result is
String if both expressions are string expressions; otherwise, result is a String variant. If both
expressions are Null, result is Null. However, if only one expression is Null, that expression is
treated as a zero-length string (" ") when concatenated with the other expression. Any
expression that is Empty is also treated as a zero-length string.
See Also
Operator precedence.
Example
This example uses the & operator to force string concatenation.
Dim MyStr
MyStr = "Hello" & " World" ' Returns "Hello World".
MyStr = "Check " & 123 & " Check" ' Returns "Check 123 Check".
* Operator
Description
Used to multiply two numbers.
Syntax
result = number1*number2
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The * operator syntax has these parts
Part Description
result Required; any numeric variable.
number1 Required; any numeric expression.
number2 Required; any numeric expression.
Remarks
The data type of result is usually the same as that of the most precise expression. The order of
precision, from least to most precise, is Byte, Integer, Long, Single, Currency, Double, and
Decimal. The following are exceptions to this order
If Then result is
Multiplication involves a converted to a Double.
Single and a Long,
The data type of result is converted to a Variant
a Long, Single, or Date containing a Double.
variant that overflows its
legal range,
The data type of result is converted to an Integer
a Byte variant that variant.
overflows its legal range,
the data type of result is converted to a Long
an Integer variant that variant.
overflows its legal range,
If one or both expressions are Null expressions, result is Null. If an expression is Empty, it is
treated as 0.
Note The order of precision used by multiplication is not the same as the order of precision
used by addition and subtraction.
See Also
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Operator precedence.
Example
This example uses the * operator to multiply two numbers.
Dim MyValue
MyValue = 2 * 2 ' Returns 4.
MyValue = 459.35 * 334.90 ' Returns 153836.315.
/ Operator
Description
Used to divide two numbers and return a floating-point result.
Syntax
result = number1/number2
The / operator syntax has these parts
Part Description
result Required; any numeric variable.
number1 Required; any numeric expression.
number2 Required; any numeric expression.
Remarks
The data type of result is usually a Double or a Double variant. The following are exceptions to
this rule
If Then result is
Both expressions are Byte, a Single unless it
Integer, or Single overflows its legal range;
expressions, in which case, an error
occurs.
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Both expressions are Byte, a Single variant unless it
Integer, or Single overflows its legal range;
variants, in which case, result is a
Variant containing a
Double.
Division involves a a Decimal data type.
Decimal and any other
data type,
One or both expressions are Null expressions, result is Null. Any expression that is Empty is
treated as 0.
See Also
Operator precedence.
Example
This example uses the / operator to perform floating-point division.
Dim MyValue
MyValue = 10 / 4 ' Returns 2.5.
MyValue = 10 / 3 ' Returns 3.333333.
\ Operator
Description
Used to divide two numbers and return an integer result.
Syntax
result = number1\number2
The \ operator syntax has these parts
Part Description
result Required; any numeric variable.
number1 Required; any numeric expression.
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