I would use Char.IsLetterOrDigit but I need the letters to be uppercase only.

I can’t seem to find a way to combine Char.IsLetterOrDigit and Char.IsUpper because digits won’t be allowed when I try this way:

if (input.All(Char.IsLetterOrDigit) && input.All(Char.IsUpper))

Am I missing something here?

How can I check each letter separately?

>Solution :

All() takes a predicate which can be a lambda expression. You can use this to check IsLetter && IsUpper separately from IsDigit.

input.All(c => (Char.IsLetter(c) && Char.IsUpper(c)) || Char.IsDigit(c))

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Alternatively, you could use a regular expression that matches zero or more uppercase characters or digits:

using System.Text.RegularExpressions;

Regex r = new Regex(@"^[A-Z0-9]*$");
r.IsMatch(input);

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Regex explanation:

^[A-Z0-9]*$
^               Start of string
 [A-Z0-9]       The uppercase letter characters or the digit characters
         *      Zero or more of the previous
          $     End of string