I'll assume, that you mean validating string versions, of these datatypes? Otherwise, regular expressions will not do much. That said, you'll probably want to look at the specifications for each language. I don't know about VB.NET, but you can find C#'s here: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csspec/html/vclrfcsharpspec_c.asp You'll notice that there only exists an "integer-literal" and "real-literal". Exactly what this is taken as, I'll assume depends on what it's either prefixed, or postfixed with, or what the context is. As such, there are no explicit regular expressions (or even implicit, the definition is grammatical, not lexical).