When you try to add two numbers of different integer types, you will get an error.
Consider the following example:
var i1: UInt8 = 255 var i2: UInt16 = 255 var i3 = i1 + i2 //cannot add two variables of different types
To fix this, you need to typecast one of the types to be the same as the other type:
var i3 = UInt16 (i1) + i2 //i3 is now UInt16