Write in an Excel cell from an application written in C#

Program.cs

using System;
using System.Runtime.InteropServices;

namespace WriteToExcel
{
    class Program
    {
        const string EXCEL_PROG_ID = "Excel.Application";

        const uint MK_E_UNAVAILABLE = 0x800401e3;

        const uint DV_E_FORMATETC = 0x80040064;

        static void Main(string[] args)
        {
            dynamic excelApp = null;
            try
            {
                excelApp = Marshal.GetActiveObject(EXCEL_PROG_ID);
            }
            catch (COMException ex)
            {
                switch ((uint)ex.ErrorCode)
                {
                    case MK_E_UNAVAILABLE:
                    case DV_E_FORMATETC:
                        // Excel n'est pas lancé.
                        break;

                    default:
                        throw;
                }
            }

            if (null == excelApp)
                excelApp = Activator.CreateInstance(Type.GetTypeFromProgID(EXCEL_PROG_ID));

            if (null == excelApp)
            {
                Console.Write("Unable to start Excel");
                return;
            }

            excelApp.Visible = true;

            dynamic workbook = excelApp.ActiveWorkbook ?? excelApp.Workbooks.Add();
            dynamic sheet = workbook.ActiveSheet;
            dynamic cell = sheet.Cells[1, 1];
            cell.Value = "Hello world!";
        }
    }
}