How read input for digits in asp.net?

I have text box for input. The user may enter number and symbols, but I need to read the input and get only digits and alpha from the input text box. How do I do it in asp.net?

Can you clarify what you are trying to do? The title of the question says you want digits; then you say you want numbers AND symbols; then you say you want digits AND alpha. What are you trying to do?

OK. So are you trying to prevent the user from entering non-permitted characters (i.e. they can ONLY enter digits and/or alphabetic characters), or are you trying to just grab the numbers and/or alphabetic characters from the user's entry, no matter what they type?

Thanks for the comments, i got it by myself.