UITextField Value Changed Event?

How can I make it so that when the contents of a text field changes, a function is called?

How can I get my UITextField value?

Just use the text attribute of the UITextField to get the value (which is a String). Then, use the toInt() method (which returns an optional) to convert that to an Integer, so that you can perform mathematical operations.

What is a UITextField?

An object that displays an editable text area in your interface.

Objective-C

[myTextField addTarget:self 
                action:@selector(textFieldDidChange:) 
      forControlEvents:UIControlEventEditingChanged];

Swift 4

myTextField.addTarget(self, action: #selector(textFieldDidChange(sender:)), for: .editingChanged)

@objc func textFieldDidChange(sender: UITextField) {...}