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private const string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\\Book1.xls;Extended Properties=\"Excel 8.0;HDR=NO;\"";
private DataSet excel()
{
    DataSet dsData = new DataSet();
    string command = "Select * from [Sheet1$]";
    OleDbConnection connection = new OleDbConnection(connectionString);
    OleDbDataAdapter adaptor = new OleDbDataAdapter(command, connection);
    adaptor.Fill(dsData);
    connection.Close();
    return dsData;
}                    

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private void Button_Click(object sender, EventArgs e)
{
    string file = "C:\\Book1.xls";
    Excel._Application xlApp;
    Excel.Workbook xlWorkbook;
    Excel.Worksheet xlWorksheet;
    Excel.Range xlRange;
 
    xlApp = new Excel.Application();
    xlWorkbook = xlApp.Workbooks.Open(file, 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t", false, false, 0, true, 1, 0);
    xlWorksheet = (Excel.Worksheet)xlWorkbook.Worksheets.get_Item(2);
 
    if (xlWorksheet.Cells[1, 2].Value != null)
    {
        TextBox1.Text = xlWorksheet.Cells[1, 2].Value.ToString();
    }

    xlWorkbook.Close();
    xlApp.Quit();
}