validate textbox is null or empty.

I have 60 textboxes  for input and  they are in 20 rows and each row has 3 textboxes (like A, B, C). all is for integer input
I want to check if A or B or C has a input value then other two must have a input integer and they can not be null or empty. But if all A and B and C are null/empty, it is valid.
What is the fast way to do that in C#? Thanks