init(_:)

The string passed as description may begin with a plus or minus sign character (+ or -), followed by one or more numeric digits (0-9).

let x = Int("123")
// x == 123

If description is in an invalid format, or if the value it denotes in base 10 is not representable, the result is nil. For example, the following conversions result in nil:

Int(" 100")                       // Includes whitespace
Int("21-50")                      // Invalid format
Int("ff6600")                     // Characters out of bounds
Int("10000000000000000000000000") // Out of range