What's wrong with this code?

Question

It's a code coach and it outputs the first character
No numerals code coach
https://code.sololearn.com/cfM0AcFpPHlh/?ref=app

Answer 1

Kevin ★ here is the code

Answer 2

Replace does not modify the original string, it returns a new string instead:

s = s.Replace(..);
Number 10 is also included in this challenge.

Answer 3

https://code.sololearn.com/cfM0AcFpPHlh/?ref=app

Answer 4

You didn't link the code...