How to remove lowercase on a textbox?

Question

I\'m trying to remove the lower case letters on a TextBox..

For example, short alpha code representing the insurance (e.g., \'BCBS\' for \'Blue Cross B

Answer 1

Here is my variant:

var input = "Blue Cross Blue Shield 12356";
var sb = new StringBuilder();
foreach (var ch in input) {
  if (char.IsUpper(ch)) { // only keep uppercase
    sb.Append(ch);
  }
}
sb.ToString(); // "BCBS"

I normally like to use regular expressions, but I don't know how to select "only uppercase" in them without [A-Z] which will break badly on characters outside the English alphabet (even other Latin characters! :-/)

Happy coding.

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But see Mr. Skeet's answer for the regex way ;-)