Is Variable Null Method

The Is Variable Null method determines if a variant variable contains a Null value. It returns one of the following values:

• -1 (negative one). The expression contains a Null value.

• 0 (zero). The expression does not contain a Null value.

A null variant does not contain data. It only identifies a result that is not valid or that is ambiguous. Null is not the same as Empty, which indicates that a variant is not yet set.

Format

IsNull(expression)

The following table describes the arguments that you can use with this method.

Argument	Description
expression	Any expression that contains a variable of data type variant.

Example

The following example asks for ten test score values and calculates the average. If any score is negative, then it sets the value to Null. This example uses the Is Variable Null method to reduce the total count of 10 scores to only the scores that contain a positive value before it calculates 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