Question

I read a string from the console. How do I make sure it only contains English characters and digits?

Answer 1

Assuming that by “English characters” you are simply referring to the 26-character Latin alphabet, this would be an area where I would use regular expressions: ^[a-zA-Z0-9 ]*$

For example:

if( Regex.IsMatch(Console.ReadLine(), "^[a-zA-Z0-9]*$") )
{ /* your code */ }

The benefit of regular expressions in this case is that all you really care about is whether or not a string matches a pattern – this is one where regular expressions work wonderfully. It clearly captures your intent, and it’s easy to extend if you definition of “English characters” expands beyond just the 26 alphabetic ones.

There’s a decent series of articles here that teach more about regular expressions.

Jørn Schou-Rode’s answer provides a great explanation of how the regular expression presented here works to match your input.