using System;
using Excel = Microsoft.Office.Interop.Excel;

namespace ExcelVirgulNoktaDegistirme
{
    class Program
    {
        static void Main(string[] args)
        {
            string excelFilePath = "C:\\path\\to\\your\\excel-file.xlsx";
            int targetColumnIndex = 2; // Örnek olarak ikinci sütunu ele alıyoruz (0 tabanlı indeksleme).

            Excel.Application excelApp = new Excel.Application();
            Excel.Workbook workbook = excelApp.Workbooks.Open(excelFilePath);
            Excel.Worksheet worksheet = workbook.Sheets[1]; // İşlem yapmak istediğiniz sayfayı seçin.

            Excel.Range usedRange = worksheet.UsedRange;
            Excel.Range targetColumn = usedRange.Columns[targetColumnIndex + 1]; // Sütun indeksini 1 artırarak ayarlayın.

            foreach (Excel.Range cell in targetColumn.Cells)
            {
                string cellValue = cell.Value?.ToString();
                if (!string.IsNullOrEmpty(cellValue))
                {
                    string newValue = cellValue.Replace(",", ".");
                    cell.Value = newValue;
                }
            }

            workbook.Save();
            workbook.Close();
            excelApp.Quit();

            System.Runtime.InteropServices.Marshal.ReleaseComObject(worksheet);
            System.Runtime.InteropServices.Marshal.ReleaseComObject(workbook);
            System.Runtime.InteropServices.Marshal.ReleaseComObject(excelApp);

            Console.WriteLine("İşlem tamamlandı.");
        }
    }
}