Delete all english letters in string

Question

I need to delete all english letters in a string.

I wrote the following code:

StringBuilder str = new StringBuilder();
foreach(var letter in test)
{   
    if(letter >= 'a' && letter <= 'z')
        continue;
    str.Append(letter); }

What is the fastest way?

Answer 1

use Regex replace method, and give it [a-z]|[A-Z]

Answer 2

Try this:

var str = test.Where(item => item < 'A' || item > 'z' || (item > 'Z' && item < 'a'));