C# :: Proper Validation Of Text Boxes?

So I am writing a multiform multiclass project for a class and I initially set out to create a validate class to check all of my text boxes. However after writing a few simple boolean functions to check if the box was empty or not, or if it was indeed an integer, decimal ect. I realized I was going to have to call these functions for every text box and also have all of my decision making based on the returned boolean variable still in the code portion of my form. I was wondering how do most people do it, should I write a class that validates the entire form at once(one form has 7 text boxes, one has 9). I suppose I am asking what would the industry standard be, how would a professional do it? While my simple functions would work, and while I could write one large function that validates them all at once both paths leave something to be desired in terms of re-usability for the entire form validation, and compact/cleanliness of code for the simple functions.

My validate class currently stands like this:

class Validate {
bool isValid = true;
int trash;
bool valid_string(string input) //parameter is textbox.text property {
if (input == string.Empty)

[Code] ......