Most of the time, you will use Int for all integers. Apple's advice is to use Int for all cases except where you need to work with a specific size of integer. Similarly, Int should be preferred to UInt even for values that cannot be negative, unless you need an unsigned integer type of the same size as the platform's native word size.
If you're not sure what that means, don't worry about it; just use Int.
The following table shows all the integer types available in Swift, along with their maximum and minimum values (unsigned minima are, of course, 0):
Integer Type |
Value |
Int.min |
-9223372036854775808 |
Int.max |
9223372036854775807 |
Int8.min |
-128 |
Int8.max |
127 |
Int16.min |
-32768 |
Int16.max |
32767 |