Conversion to string types from Double and Float in Swift

let exp = 2.718_281_828

let s1 = "\(exp)"
//s1 is 2.718281828

let s2 = String(format: "%0.3f", exp)
//s2 is 2.718

let s3 = String(format: "%0.2E", exp / 100)
//s3 is 2.72E-02