using System;
using System.Collections.Generic;
using System.Text;
using System.Diagnostics;
using Bytescout.Spreadsheet;

namespace HelloWorld
{
class Program
{
static void Main(string[] args)
{
// Create new Spreadsheet
Spreadsheet document = new Spreadsheet();

// Get worksheet by name
Worksheet worksheet = document.Workbook.Worksheets.Add("Sample");

// Set captions
worksheet.Cell(0, 0).Value = "#";
worksheet.Cell(0, 1).Value = "Date";

for (int i = 1; i < 8; i++)
{
// Set number
worksheet.Cell(i, 0).Value = i;

// Set current cell
Cell currentCell = worksheet.Cell(i, 1);

// Set date. This is days since 01.01.1900
// You can also convert number to date time using the function: DateTime.FromOADate(double d)
currentCell.Value = 30000 + i * 1000;

// Set date format
currentCell.NumberFormat = "dd.mm.yyyy";
}

// Save document
document.SaveAs("Sample.xls");

// Close document
document.Close();

// open generated XLS document in default program
Process.Start("Sample.xls");
}
}
}

Download example source code: bytescoutxls_date_formatting_for_cells.zip (8 KB)