swift2.2StringCS193P-playground

import Foundation

var s = "hello"
s.startIndex // starts at 0

let index = s.startIndex.advancedBy(2) // index is a String.index to the 3rd glyph, "l"
print (index)

s.insertContentsOf("abc".characters, at: index)

let startIndexPlusOne = s.startIndex.advancedBy(1) // advance s.startIndex from 0 to 1
let endIndex = s.startIndex.advancedBy(6) // advance s.startIndex from 0 to 6

let substring = s[index..<endIndex] // "abcl"