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Function to check the format of a telephone number (VB ASP.NET)

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Source Code

Since database formats need to be consistent, I found this routine necessary since many people have different thoughts on how a telephone number is written. This function checks to see if the contents of a text box conforms to a telephone number format (xxx-xxx-xxxx). The function accepts a string as the input parameter and returns true or false. Click here to download a sample aspx page

function CheckPhoneNumber(strPhoneNumber As String)
 ' This function tests to see if a string is a telephone number 
 ' formatted (xxx-xxx-xxxx) and insures that they are numbers.
	
 ' First we set the result to false, assume all the tests fail 	
 CheckPhoneNumber = False
	
 ' Test to see if there are 12 characters in the string
 if strPhoneNumber.Length <> 12 then
	exit function
 end if
	
 ' Turn the sting that was passed into an array
 Dim aPhoneNumber() As String = strPhoneNumber.Split("-")
	
 ' Now we see if there are three strings in the array
 if aPhoneNumber.Length <> 3 then
	aPhoneNumber = nothing
	exit function
 end if
	
 ' Now we see if the three individual strings are numbers	
 for i As Integer = 0 to 2
	if NOT IsNumeric(aPhoneNumber(i)) then		
		aPhoneNumber = nothing
		i = nothing	
		exit function
	end if
 next i
	
 ' Now we make sure the individual strings are the correct length
 if (aPhoneNumber(0).Length <> 3) OR _
	 (aPhoneNumber(1).Length <> 3) OR _
	  (aPhoneNumber(2).Length <> 4) then
	  	aPhoneNumber = nothing		
		exit function
 end if
	
 ' Clean Up
 aPhoneNumber = nothing	

 ' If we got here then the string is in the correct format
 CheckPhoneNumber = True
end function