Operation between hours

Question

I have 2 buttons, when I click each button a timepicker comes out and return the time in the button. I have 2 text field and 1 label. In textfield 1 I put a number that will be

Answer 1

Create NSDate objects that have the same date part, but with the time set to the times in the buttons.

To subtract dates, use

 NSTimeInterval seconds = [date timeIntervalSinceDate:otherDate];

NSTimeInterval is just a number, you can multiply it. First multiply by 60*60 to get it to hours. Then multiply it by the number on your multiplier button.