static string CommonCharacters(string str1, string str2)
        {
            var ListofCommonCharactersAlreadyIncluded = new List<char>();
            string commoncharacters = "";
            for (int i = 0; i < str1.Length; i++)
            {
                for (int j = 0; j < str2.Length; j++)
                {
                    if((str1[i]==str2[j])&&(!ListofCommonCharactersAlreadyIncluded.Contains(str1[i])))

                    {
                        commoncharacters += str1[i] + " ";
                        ListofCommonCharactersAlreadyIncluded.Add(str1[i]);

                    }


                }
            }


        }