Day4 String Change Too Much ,so delay learning the string

//                                          **Day4

//                                          **String Range

//var str = "hello world  i‘m glad to see your achievement world"

//let number = str.characters.count

//let str2 = "yes my goal is not change"

//str.rangeOfString("world")

//str.rangeOfString("world", options: NSStringCompareOptions.BackwardsSearch)

//str2.rangeOfString("goal", options: NSStringCompareOptions.CaseInsensitiveSearch)

// summary   ignore A or a to search use CaseInsensiticeSearch

// summary   search from the end of string use method backwardsSearch

// range

//var str : String = "mymymy"

//str.rangeOfString("my")

//str.rangeOfString("my", options: NSStringCompareOptions.BackwardsSearch)

//

//str.startIndex

//str.endIndex

//let strRange = Range<String.Index>(start: str.startIndex , end: str.endIndex)

//

//let startIndex:String.Index = str.startIndex

//let searchIndex = Range<String.Index>(start:str.startIndex,end: str.endIndex)

//str.rangeOfString("my", options: NSStringCompareOptions.CaseInsensitiveSearch, range: searchIndex)

// substring

//var newString = "tang666"

//let startIndex = newString.startIndex

//let endIndex = newString.endIndex