Try this.
string[] arr;
arr = "123,456,678".Split(',');
OP: I'm doing code in VB.NET tell me, user enters a,b,c,d in text box, how can I insert a b c d separately into database
Dim arr As String()
arr = "123,456,789".Split(",")
Dim strval As String = ""
For i As Integer = 0 To arr.Length - 1
strval = arr(i)
Next