Simple expression

Question

I am convinced that this requirement is so simple it's embarrassing to ask but for some reason it is escaping me, perhaps I don't know enough about Regular Expressions. :)
All I need to do is validate a string which needs to match 1-4 numbers followed optionally by a single letter (upper or lower case a-z). so 9, 8a, 225z are all valid but, a, 2ab, 12345a, are invalid.
All help very welcome!

ps I have no idea what I'm wanted to enter under "Tags" so I just picked one at random!

Answer 1

Try this simple expression too:

^[0-9]{1,4}[a-zA-Z]?$

Answer 2

Please try if this can meet your needs:

            Regex regex = new Regex(@"(?<=^[0-9]{1,3}(?:a|A|z|Z|$)\b)");  
            string test = "123a";  
            bool re = regex.IsMatch(test);  

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