I have windows form. There are many controls present in form. All controls will fill with values when form load. All controls are editable say textbox, dropdownlist, radio buttons, etc. at bottom there is update button. 

When user change value and press update button updated values will save.

But sometimes user haven't change any value and press update.

So now, How to know user not changed any value to update?
Is there any standard way to know, user edited but not change any existing value?

Note: I don't want to check all values one by one.