C# string to int with complex structure

  string expr = "1+23+45+65+55+12";
 
  string[] num = expr.Split(new char[] { '+' });
  int sum = 0;
  foreach (var s in num)
  {
    sum += int.Parse(s);
  }
  Console.WriteLine("sum =  {0}", sum);

public static double Evaluate(string expression)
        {
            System.Data.DataTable table = new System.Data.DataTable();
            table.Columns.Add("expression", string.Empty.GetType(), expression);
            System.Data.DataRow row = table.NewRow();
            table.Rows.Add(row);
            return double.Parse((string)row["expression"]);
        }