What does this
translateButton.Click += (object sender, EventArgs e) =>
translatedNumber = Core.PhonewordTranslator.ToNumber(phoneNumberText.Text);
callButton.Text = "Call";
callButton.Enabled = false;
callButton.Text = "Call " + translatedNumber;
callButton.Enabled = true;
As an arithmetic operation
add/subtract the right side to/from the left side and assign the result to the left side.
a += 5 is the same as writing
a = a + 5.
This code, however, is about events and event handlers. In the context of event handlers,
add/remove the following delegate to/from the list of event handlers for this event.
So your sample code adds a new event handler to the button's
Click event. The way it is written is called inline implementation.
Please note that in the context of event handlers, you can usually not replace
Event += Handler;
Event = Event + Handler;
as there is no way to "read" the
Event "property" outside the implementing class.