Reading Excel Spreadsheets with C# and ADO.Net

using System;
using System.Data.OleDb;

namespace ConsoleApplication1
{
  class Program
  {
    static void Main()
    {
      string connectionString = "Provider=Microsoft.Jet.OleDb.4.0; data source=c:customers.xls; Extended Properties=Excel 8.0;";

      // Select using a Named Range
      string selectString = "SELECT * FROM Customers";

      // Select using a Worksheet name
      string selectString = "SELECT * FROM [Sheet1$]";

      OleDbConnection con = new OleDbConnection(connectionString);
      OleDbCommand cmd = new OleDbCommand(selectString,con);

      try
      {
        con.Open();
        OleDbDataReader theData = cmd.ExecuteReader();
        while (theData.Read())
        {
          Console.WriteLine("{0}: {1} ({2}) - {3} ({4})", theData.GetString(0),theData.GetString(1),theData.GetString(2),theData.GetString(3),theData.GetString(4));
        }
      }
      catch (Exception ex)
      {
        Console.WriteLine(ex.Message);
      }
      finally
      {
        con.Dispose();
      }
    }
  }
}

string connectionString = "Provider=Microsoft.Jet.OleDb.4.0; data source=c:customers.xls; Extended Properties=Excel 8.0;";
string selectString = "INSERT INTO Customers VALUES('12345', 'Acme Inc', 'Acme Way, CA', 'Testy McTest', '01234-987654')";

OleDbConnection con = new OleDbConnection(connectionString);
OleDbCommand cmd = new OleDbCommand(selectString, con);

try
{
  con.Open();
  cmd.ExecuteNonQuery();
}
catch (Exception ex)
{
  Console.WriteLine(ex.Message);
}
finally
{
  con.Dispose();
}