PurplePen.ChangeAllCodes.FindDuplicateCodes C# (CSharp) Method

        int FindDuplicateCodes()
        {
            Dictionary<string, int> dict = new Dictionary<string, int>();        // dictionary to map code string to row number.

            for (int row = 0; row < grid.Rows.Count; ++row) {
                string code = (string) (grid[1, row].Value);
                if (dict.ContainsKey(code))
                    return dict[code];         // already present, return the row number.
                else
                    dict[code] = row;
            }

            return -1;     // no problem.
        }