دستورات مرتبط با بررسی وضعیت مقادیر در VB

Values

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دستور نوشتاری فرمان(Syntax) به نحو زیر است:

IsNull
Returns a Boolean value that indicates whether an expression contains no valid data (Null).
Syntax
IsNull(expression)
The required expression argument is a Variant containing a numeric expression or string expression.
Remarks
IsNull returns True if expression is Null; otherwise, IsNull returns False. If expression consists of
more than one variable, Null in any constituent variable causes True to be returned for the entire
expression
Example:
MyVar = ""
MyCheck = IsNull(MyVar) ' Returns False.
MyVar = Null
MyCheck = IsNull(MyVar) ' Returns True.

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دستور نوشتاری فرمان(Syntax) به نحو زیر است:

IsEmpty
Returns a Boolean value indicating whether a variable has been initialized.
Syntax
IsEmpty(expression)
The required expression argument is a Variant containing a numeric or string expression. However,
because IsEmpty is used to determine if individual variables are initialized, the expression argument is
most often a single variable name.
Remarks
IsEmpty returns True if the variable is uninitialized, or is explicitly set to Empty; otherwise, it returns
False. False is always returned if expression contains more than one variable. IsEmpty only returns
meaningful information for variants.
Example:
MyVar = Null ' Assign Null.
MyCheck = IsEmpty(MyVar) ' Returns False.
MyVar = Empty ' Assign Empty.
MyCheck = IsEmpty(MyVar) ' Returns True.

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دستور نوشتاری فرمان(Syntax) به نحو زیر است:

IsNumeric
Returns a Boolean value indicating whether an expression can be evaluated as a number.
Syntax
IsNumeric(expression)
The required expression argument is a Variant containing a numeric expression or string expression.
Remarks
IsNumeric returns True if the entire expression is recognized as a number; otherwise, it returns False.
IsNumeric returns False if expression is a date expression.
Example:
MyVar = "459.95" ' Assign value.
MyCheck = IsNumeric(MyVar) ' Returns True.
MyVar = "45 Help" ' Assign value.
MyCheck = IsNumeric(MyVar) ' Returns False.