title: i want int in my textbox and in my other i want string with "if"
body: <p>I'm new using c#</p>
  
  <p>So in my textbox postal code. I want that i only can use int (1,2,3,4,...) and it may only be 4 numbers. How can i do that?</p>
  
  <p>And what happens with that when you need to fill in your birthday?</p>
  
  <p>And what happens when you fill in a email? (test47@hotmail.com)</p>
  
  <p>So my next question is: In my textbox Name, i want that i only can use string (Paul, Tom, ...). How can i do that?</p>
  
  <p>It must be with an "if". Not with try &amp; catch</p>
  
  <p>Thanks for helping me!</p>