how to split a string without using split function in c#

Use regex something like this,

string strRegex = @"[\s]+"; // splits by space.
RegexOptions myRegexOptions = RegexOptions.IgnoreCase | RegexOptions.Multiline;
Regex myRegex = new Regex(strRegex, myRegexOptions);
string strTargetString = @"Example String.";

foreach (Match myMatch in myRegex.Matches(strTargetString))
{
  if (myMatch.Success)
  {
        var str = myMatch.Group[1].Value; //Add this value to list.
    // Add your code here
  }
}

string str = "this is a test string";
            ArrayList ar = new ArrayList();
            string tmp = "";
            for (int i = 0; i            {
              
                if (str[i] != ' ')
                {
                    tmp = tmp + str[i];
                    continue;
                }

              
                ar.Add(tmp);
                tmp = "";
            }
            foreach (string a in ar)
            {
                Console.WriteLine(a );
               
            }
            Console.ReadLine();

here i have split based on space.