extract numbers and alpha into two strings

extract numbers and alpha into two strings

Suppose I have a string that looks like this: "dentist: 800-483-9767" and
that's max 25 characters. I want to extract the digits and letters
characters into 2 strings so that I get this:
string digits = "8004839767";
string letters = "dentist";
What's the best what to do this?
Thanks