For example: Julius Caesar protected his confidential information by encrypting it in a cipher. Caesar’s cipher rotated every letter in a string by a fixed number, K, making it unreadable by his enemies. Given a string,S , and a number,K , encrypt S.

Note: The cipher only encrypts letters; symbols, such as -, remain unencrypted.

func cipher(messageToCipher: String, k: Int)-> String{   var  eMessage = ""   let arr = messageToCipher.characters.map { String($  0) }   for ch in arr {     for code in String(ch).utf8 {          if (65<=code && code<=90) || (97<=code && code<=122) {               if k > 26{                     let value =  k % 26 == 0 ? k / 26 : k % 26                      var pCode  = ((Int(code))  + (value))                        if (pCode  > 122 && (97<=code && code<=122)) || (pCode  > 90 && (65<=code && code<=90)) {                         pCode = pCode - 26                     }                     let s = String(UnicodeScalar(UInt8(pCode)))                    eMessage = eMessage + s                 }else                 {                     var pCode  = Int(code) + k                      if (pCode  > 122 && (97<=code && code<=122)) || (pCode  > 90 && (65<=code && code<=90)) {                         pCode = pCode - 26                     }                     let s = String(UnicodeScalar(UInt8(pCode)))                    eMessage = eMessage + s                 }          }         else{                     eMessage = eMessage + ch         }     }      }   return eMessage }   print(cipher(messageToCipher: "abc", k: 2) ) 

I solved this way and it was passed all test case

More information this problem set : Caesar Cipher