14032019_1

import Foundation

extension String{
    mutating func  surround(_ s:String){
        self = "\(s)\(self)\(s)"
    }
}

var st = "welcome"
st.surround(" ***** ")
print(st)

extension Int{
    mutating func  exp(_ e:Int){
        self = Int(pow(Double(self),Double(e)))
    }
}

var num = 5
num.exp(2)
print(num)