public class Workbook 

using( var doc = Workbook.Load( "test.xlsx") ) // Loads an existing Workbook named “test.xlsx”.
  {
    var worksheet = doc.Worksheets[ 1 ]; // Gets the second worksheet. 
    worksheet.Cells[ “A2” ].Value = 12;  // Sets a value in “A2”.
    var stream = new MemoryStream();
    doc.SaveAs( stream); // Saves the result in a stream.
  }

    var stream = new MemoryStream();
    using( var doc = Workbook.Create( stream ) ) // Creates a workbook in a stream.
  {
    var worksheet = doc.Worksheets[ 1 ]; // Gets the second worksheet. 
    worksheet.Cells[ “A2” ].Value = 12; // Sets a value in “A2”.
    worksheet.Columns[ 1 ].Cells[ 0 ].Formula = “=SUM(A1:A2)”; //Sets a formula in “B1”.
    doc.CalculateFormulas(); // Calculate the Value of “B1”, which contains a formula and for all other Worksheets containing cells with formulas.
    doc.Save(); // Saves the Workbook in the stream.
  }