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IsNull Function

This standard VB function is used to determine whether a variant variable has the Null value.

Syntax

IsNull(expression)

Returns

-1 (TRUE) if a variant expression contains the Null value, 0 (FALSE) otherwise.

Usage

Null variants have no associated data and serve only to represent invalid or ambiguous results. Null is not the same as Empty, which indicates that a variant has not yet been initialized.

Example

This example asks for ten test score values and calculates the average. If any score is negative, the value is set to Null. Then IsNull is used to reduce the total count of scores (originally 10) to just those with positive values before calculating the average.

Sub Button_Click
   Dim arrayvar(10)
   Dim count as Integer
   Dim total as Integer
   Dim x as Integer
   Dim tscore as Single
   count = 10
   total = 0
   For x = 1 to count
      tscore = 88
      If tscore<0 then
         arrayvar(x) = Null
      Else
         arrayvar(x) = tscore
         total = total + arrayvar(x)
      End If
   Next x
   Do While x <> 0
      x = x - 1
      If IsNull(arrayvar(x)) = -1 then
         count = count-1
      End If
   Loop
   msgtext = "The average (excluding negative values) is: "
      msgtext = msgtext & Chr(10) & Format(total/count, "##.##")
End Sub

See Also

IsDate Function
IsEmpty Function
IsNumeric Function
VarType Function