arcgis desktop - Handling NULL values when using CInt?

This expression works perfectly when integer fields are 0 instead of NULL but now I am working with a GDB that has many NULL values. I'm not sure how to force CInt to only run if field is not null.

Function FindLabel ( [SQFT_CONC] , [DEPTH_CONC] , [SQFT_ASPHT] , [DEPTH_ASHT]  )
  Dim strInput
  Dim dc
  Dim da
  dc = CInt([DEPTH_CONC])

  da = CInt([DEPTH_ASHT])
  val = dc + da
  if (val = 10) then
     strInput = "IT WORKS"
  end if

  FindLabel = strInput
End Function

Answer

I found the correct way do handle this. If the field is Null then it will count as a 0. This first way is shorter although I'm not sure if it will give the desired result in every scenario.

Function FindLabel ( [SQFT_CONC] , [DEPTH_CONC] , [SQFT_ASPHT] , [DEPTH_ASHT]  )
  Dim strInput
  Dim dc
  Dim da
  dc = CInt(0 & [DEPTH_CONC])
  da = CInt(0 & [DEPTH_ASHT])
  val = dc + da
  if (val = 10) then
     strInput = "IT WORKS"
  end if


  FindLabel = strInput
End Function

Alternatively....

To treat Null values as 0 check for Null and substitute a 0 into the variable.

Function FindLabel ( [SQFT_CONC] , [DEPTH_CONC] , [SQFT_ASPHT] , [DEPTH_ASHT]  )
  Dim strInput
  Dim dc
  Dim da

  if isNull([DEPTH_CONC]) then
    dc = 0
  else
    dc = CInt([DEPTH_CONC])
  end if
  if isNull([DEPTH_ASHT]) then
    da = 0
  else
    da = CInt([DEPTH_ASHT])
  end if

  val = dc + da
  if (val = 10) then
     strInput = "IT WORKS"
  end if

  FindLabel = strInput
End Function

To ignore records completely, step over them in an if statement if either value is Null

Function FindLabel ( [SQFT_CONC] , [DEPTH_CONC] , [SQFT_ASPHT] , [DEPTH_ASHT]  )

  Dim strInput
  Dim dc
  Dim da
  if not isNull([DEPTH_CONC]) and not isNull([DEPTH_ASHT]) then
    dc = CInt([DEPTH_CONC])
    da = CInt([DEPTH_ASHT])
    val = dc + da
    if (val = 10) then
       strInput = "IT WORKS"
    end if

  end if
  FindLabel = strInput
End Function