swift 3.0 version
//: Playground - noun: a place where people can play
import UIKit
var str = "Welcome to Play Swift! Step by Step learn Swift language from now!"
// range
str.rangeOfString("Step")
str.rangeOfString("Step", options: NSStringCompareOptions.BackwardsSearch)
str.rangeOfString("welcome", options: NSStringCompareOptions.CaseInsensitiveSearch)
str.startIndex
str.endIndex
let strRage = Range<String.Index>(str.startIndex..<str.endIndex)
let startIndex = str.startIndex
let endIndex:String.Index = str.startIndex.advancedBy(10)
let searchRange = Range<String.Index>(startIndex..<endIndex)
str.rangeOfString("Step", options: NSStringCompareOptions.CaseInsensitiveSearch, range: searchRange)
//substring
var toIndex = str.startIndex.advancedBy(4)
str.substringToIndex(toIndex)
var fromIndex = str.startIndex.advancedBy(14)
str.substringFromIndex(fromIndex)
str.substringWithRange(Range<String.Index>(toIndex..<fromIndex))
//insert
var insertIndex = str.startIndex.advancedBy(22)
str.insert("!", atIndex: insertIndex)
//remove
str.removeAtIndex(insertIndex)
str
str.removeRange(Range<String.Index>(str.startIndex..<insertIndex))
//replace
var replaceEndIndex = str.startIndex.advancedBy(13)
str.stringByReplacingCharactersInRange(Range<String.Index>(str.startIndex..<replaceEndIndex), withString: "Step-by-step")
运行效果图: