The sample demonstrates how to provide a dropdownlist for valid data

                     
using System;

using Spire.Xls;

namespace DropDownList
{
    class Program
    {
        private static void CreateSampleData(Worksheet sheet)
        {
            sheet.Range["D8"].Text = "Country";
            //set the datasource of the E8
            sheet.Range["X1"].Text = "Lucy";
            sheet.Range["X2"].Text = "Bolivia";
            sheet.Range["X3"].Text = "Brazil";
            sheet.Range["X4"].Text = "Canada";
            sheet.Range["X5"].Text = "Chile";
            sheet.Range["X6"].Text = "Colombia";
            sheet.Range["X7"].Text = "Cuba";
            sheet.Range["X8"].Text = "Ecuador";
            sheet.Range["X9"].Text = " Salvado";
            sheet.Range["X10"].Text = "Guyana";
            sheet.Range["X11"].Text = "Jamaicatates";
            sheet.Range["X12"].Text = "Mexico";
            sheet.Range["X13"].Text = "Nicaragua";
            sheet.Range["X14"].Text = "Paraguay";
            sheet.Range["X15"].Text = "Peru";
            sheet.Range["X16"].Text = "United";
            sheet.Range["X17"].Text = "Uruguay";
            sheet.Range["X18"].Text = "Venezuel";

            CellRange rangeName = sheet.Range["E8"];
            rangeName.DataValidation.AllowType = CellDataType.Formula;
            rangeName.DataValidation.DataRange = sheet.Range["X1:X18"];
            rangeName.DataValidation.IgnoreBlank = true;
            rangeName.Activate();
            //hide column X                                 
            sheet.HideColumn(sheet.Range["X1"].Column);

            sheet.Range["D10"].Text = "Capital";
            //set the datasource of the E9
            sheet.Range["Y1"].Text = "Buenos Aires";
            sheet.Range["Y2"].Text = "La Paz";
            sheet.Range["Y3"].Text = "Brasilia";
            sheet.Range["Y4"].Text = "Ottawa";
            sheet.Range["Y5"].Text = "Santiago";
            sheet.Range["Y6"].Text = "Bagota";
            sheet.Range["Y7"].Text = "Havana";
            sheet.Range["Y8"].Text = "Quito";
            sheet.Range["Y9"].Text = "San Salvador";
            sheet.Range["Y10"].Text = "Georgetown";
            sheet.Range["Y11"].Text = "Kingston";
            sheet.Range["Y12"].Text = "Mexico City";
            sheet.Range["Y13"].Text = "Managua";
            sheet.Range["Y14"].Text = "Asuncion";
            sheet.Range["Y15"].Text = "Lima";
            sheet.Range["Y16"].Text = "Washington";
            sheet.Range["Y17"].Text = "Montevideo";
            sheet.Range["Y18"].Text = "Caracas";
            //Binding the datasource                 
            CellRange rangeCapital = sheet.Range["E10"];
            rangeCapital.DataValidation.AllowType = CellDataType.Formula;
            rangeCapital.DataValidation.DataRange = sheet.Range["Y1:Y18"];
            rangeCapital.DataValidation.IsSuppressDropDownArrow = false;
            rangeCapital.Activate();
            //hide coulumn Y
            sheet.HideColumn(sheet.Range["Y1"].Column);

            sheet.Range["D12"].Text = "Continent";
            //set the datasource of the F9
            CellRange rangeContinent = sheet.Range["E12"];
            rangeContinent.DataValidation.AllowType = CellDataType.Formula;
            rangeContinent.DataValidation.Values = new String[] { "South America", "North America" };
            rangeContinent.DataValidation.IsSuppressDropDownArrow = false;
            rangeContinent.Activate();

            //Set the column's width
            sheet.Range["E8"].Text = "Please select the country";
            sheet.Range["E10"].Text = "Please select the capital";
            sheet.Range["E12"].Text = "Please select the con tinent";
            sheet.AutoFitColumn(4);
            sheet.AutoFitColumn(5);

            //Style
            sheet.Range["D8:D12"].Style.Font.IsBold = true;
            sheet.Range["D8"].Style.KnownColor = ExcelColors.Color36;
            sheet.Range["D10"].Style.KnownColor = ExcelColors.Color36;
            sheet.Range["D12"].Style.KnownColor = ExcelColors.Color36;
            sheet.Range["E8"].Style.KnownColor = ExcelColors.LightGreen1;
            sheet.Range["E10"].Style.KnownColor = ExcelColors.LightGreen1;
            sheet.Range["E12"].Style.KnownColor = ExcelColors.LightGreen1;

            sheet.SetRowHeight(8, 16);
            sheet.SetRowHeight(10, 16);
            sheet.SetRowHeight(12, 16);
        }
        static void Main(string[] args)
        {
            //Build the workbook
            Workbook workbook = new Workbook();
            workbook.CreateEmptySheets(1);
            Worksheet sheet = workbook.Worksheets[0];
            sheet.GridLinesVisible = false;

            //Write sample data
            CreateSampleData(sheet);
            workbook.SaveToFile("test.xls");
            System.Diagnostics.Process.Start(workbook.FileName);
        }
    }
}                                                                                                                                                                                                                                              

                                                                                                          
Imports Spire.Xls

Module Module1
    Private Sub CreateSampleData(ByVal sheet As Worksheet)
        sheet.Range("D8").Text = "Country"
        'Set the datasource of D9
        sheet.Range("X1").Text = "Lucy"
        sheet.Range("X2").Text = "Bolivia"
        sheet.Range("X3").Text = "Brazil"
        sheet.Range("X4").Text = "Canada"
        sheet.Range("X5").Text = "Chile"
        sheet.Range("X6").Text = "Colombia"
        sheet.Range("X7").Text = "Cuba"
        sheet.Range("X8").Text = "Ecuador"
        sheet.Range("X9").Text = " Salvado"
        sheet.Range("X10").Text = "Guyana"
        sheet.Range("X11").Text = "Jamaicatates"
        sheet.Range("X12").Text = "Mexico"
        sheet.Range("X13").Text = "Nicaragua"
        sheet.Range("X14").Text = "Paraguay"
        sheet.Range("X15").Text = "Peru"
        sheet.Range("X16").Text = "United"
        sheet.Range("X17").Text = "Uruguay"
        sheet.Range("X18").Text = "Venezue"

        'Binding the datasource of D9
        Dim rangeCountry As CellRange = sheet.Range("E8")
        rangeCountry.DataValidation.AllowType = CellDataType.Formula
        rangeCountry.DataValidation.DataRange = sheet.Range("X1:X18")
        rangeCountry.DataValidation.IsSuppressDropDownArrow = False
        rangeCountry.DataValidation.IgnoreBlank = True
        rangeCountry.Activate()
        sheet.HideColumn(sheet.Range("X1").Column)

        sheet.Range("D10").Text = "Capital"
        'Set the datasource of E9
        sheet.Range("Y1").Text = "Buenos Aires"
        sheet.Range("Y2").Text = "La Paz"
        sheet.Range("Y3").Text = "Brasilia"
        sheet.Range("Y4").Text = "Ottawa"
        sheet.Range("Y5").Text = "Santiago"
        sheet.Range("Y6").Text = "Bagota"
        sheet.Range("Y7").Text = "Havana"
        sheet.Range("Y8").Text = "Quito"
        sheet.Range("Y9").Text = "San Salvador"
        sheet.Range("Y10").Text = "Georgetown"
        sheet.Range("Y11").Text = "Kingston"
        sheet.Range("Y12").Text = "Mexico City"
        sheet.Range("Y13").Text = "Managua"
        sheet.Range("Y14").Text = "Asuncion"
        sheet.Range("Y15").Text = "Lima"
        sheet.Range("Y16").Text = "Washington"
        sheet.Range("Y17").Text = "Montevideo"
        sheet.Range("Y18").Text = "Caracas"

        'Binding the datasource of E9
        Dim rangeCapital As CellRange = sheet.Range("E10")
        rangeCapital.DataValidation.AllowType = CellDataType.Formula
        rangeCapital.DataValidation.DataRange = sheet.Range("Y1:Y18")
        rangeCapital.DataValidation.IsSuppressDropDownArrow = False
        rangeCapital.DataValidation.IgnoreBlank = True
        rangeCapital.Activate()
        sheet.HideColumn(sheet.Range("Y1").Column)

        sheet.Range("D12").Text = "Continent"
        'Set the datasource of F9
        Dim rangeContinent As CellRange = sheet.Range("E12")
        rangeContinent.DataValidation.AllowType = CellDataType.Formula
        rangeContinent.DataValidation.Values = New String() {"South America", "North America"}
        rangeContinent.DataValidation.IsSuppressDropDownArrow = False
        rangeContinent.Activate()

        'Set the width of the column
        sheet.Range("E8").Text = "Please select the country "
        sheet.Range("E10").Text = "Please select the capital "
        sheet.Range("E12").Text = "Please select the continent "
        sheet.AutoFitColumn(4)
        sheet.AutoFitColumn(5)

        'Style                                                            
        sheet.Range("D8:D12").Style.Font.IsBold = True
        sheet.Range("D8").Style.KnownColor = ExcelColors.Color36
        sheet.Range("D10").Style.KnownColor = ExcelColors.Color36
        sheet.Range("D12").Style.KnownColor = ExcelColors.Color36
        sheet.Range("E8").Style.KnownColor = ExcelColors.LightGreen1
        sheet.Range("E10").Style.KnownColor = ExcelColors.LightGreen1
        sheet.Range("E12").Style.KnownColor = ExcelColors.LightGreen1
        sheet.SetRowHeight(8, 16)
        sheet.SetRowHeight(10, 16)
        sheet.SetRowHeight(12, 16)
    End Sub

    Sub Main()
        Dim workbook As Workbook = New Workbook()
        workbook.CreateEmptySheet(1)
        Dim sheet As Worksheet = workbook.Worksheets(0)
        sheet.GridLinesVisible = False
        'Writes sample data
        CreateSampleData(sheet)
        workbook.SaveToFile("test.xls")
        System.Diagnostics.Process.Start(workbook.FileName)
    End Sub

End Module                                                                                        

The sample demonstrates how to read data with fomulas

using System.IO;
using System.Windows.Forms;
using System;
using System.Data;
using Spire.Xls;

namespace DataReadWithFormulas
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable dataTable = new DataTable();
            using (Stream buffer = WriteFormulas())
            {
                //load
                Workbook workbook = new Workbook();
                workbook.LoadFromStream(buffer);
                //calculate all cells' formula
                workbook.CalculateAllValue();
                //read cells' value to data table
                Worksheet sheet = workbook.Worksheets[0];
                dataTable.Columns.Add("Formulas", typeof(String));
                dataTable.Columns.Add("Results", typeof(Object));
                foreach (CellRange row in sheet["A5:B46"].Rows)
                {
                    String formula = row.Columns[1].Formula;
                    Object value = row.Columns[1].FormulaValue;
                    dataTable.Rows.Add(formula, value);
                }
            }
            using (Form frm1 = new Form())
            {
                DataGrid dataGrid = new DataGrid();
                dataGrid.CaptionVisible = false;
                dataGrid.ReadOnly = true;
                dataGrid.DataSource = dataTable;
                dataGrid.Dock = DockStyle.Fill;

                frm1.Text = "Data Export with Formulas";
                frm1.Width = 480;
                frm1.Height = 360;
                frm1.StartPosition = FormStartPosition.CenterParent;
                frm1.Controls.Add(dataGrid);
                frm1.ShowDialog();
            }
        }

        private static Stream WriteFormulas()
        {
            //Create Excel files
            Workbook workbook = new Workbook();
            Worksheet sheet = workbook.Worksheets[0];//it's the first sheet of the worksheets

            int currentRow = 1;
            string currentFormula = string.Empty;
            sheet.SetColumnWidth(1, 32);//SetColumnWidth(columnIndex,width);
            sheet.SetColumnWidth(2, 16);
            sheet.SetColumnWidth(3, 16);
            sheet.Range[currentRow++, 1].Value = "Examples of formulas :";
            sheet.Range[++currentRow, 1].Value = "Test data:";

            CellRange range = sheet.Range["A1"];
            range.Style.Font.IsBold = true;
            range.Style.FillPattern = ExcelPatternType.Solid;
            range.Style.KnownColor = ExcelColors.LightGreen1;
            range.Style.Borders[BordersLineType.EdgeBottom].LineStyle = LineStyleType.Medium;

            //test data
            sheet.Range[currentRow, 2].NumberValue = 7.3;
            sheet.Range[currentRow, 3].NumberValue = 5; ;
            sheet.Range[currentRow, 4].NumberValue = 8.2;
            sheet.Range[currentRow, 5].NumberValue = 4;
            sheet.Range[currentRow, 6].NumberValue = 3;
            sheet.Range[currentRow, 7].NumberValue = 11.3;

            sheet.Range[++currentRow, 1].Value = "Formulas"; ;
            sheet.Range[currentRow, 2].Value = "Results";
            range = sheet.Range[currentRow, 1, currentRow, 2];

            //range.Value = "Formulas";
            range.Style.Font.IsBold = true;
            range.Style.KnownColor = ExcelColors.LightGreen1;
            range.Style.FillPattern = ExcelPatternType.Solid;
            range.Style.Borders[BordersLineType.EdgeBottom].LineStyle = LineStyleType.Medium;

            //str.
            currentFormula = "=\"hello\"";
            sheet.Range[++currentRow, 1].Text = "=\"hello\"";
            sheet.Range[currentRow, 2].Formula = currentFormula;
            sheet.Range[currentRow, 3].Formula = "=\"\u4f60\u597d\"";

            //int.
            currentFormula = "=300";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;

            // float                        
            currentFormula = "=3389.639421";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;

            //bool.
            currentFormula = "=false";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;

            currentFormula = "=1+2+3+4+5-6-7+8-9";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;

            currentFormula = "=33*3/4-2+10";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;


            // sheet reference
            currentFormula = "=Sheet1!$B$3";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;

            // sheet area reference
            currentFormula = "=AVERAGE(Sheet1!$D$3:G$3)";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;

            // Functions
            currentFormula = "=Count(3,5,8,10,2,34)";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;


            currentFormula = "=NOW()";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow, 2].Formula = currentFormula;
            sheet.Range[currentRow, 2].Style.NumberFormat = "yyyy-MM-DD";

            currentFormula = "=SECOND(11)";
            sheet.Range[++currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=MINUTE(12)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=MONTH(9)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=DAY(10)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=TIME(4,5,7)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=DATE(6,4,2)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=RAND()";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=HOUR(12)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=MOD(5,3)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=WEEKDAY(3)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=YEAR(23)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=NOT(true)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=OR(true)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=AND(TRUE)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=VALUE(30)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=LEN(\"world\")";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=MID(\"world\",4,2)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=ROUND(7,3)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=SIGN(4)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=INT(200)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=ABS(-1.21)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=LN(15)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=EXP(20)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=SQRT(40)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=PI()";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=COS(9)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=SIN(45)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=MAX(10,30)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=MIN(5,7)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=AVERAGE(12,45)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=SUM(18,29)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            currentFormula = "=IF(4,2,2)";
            sheet.Range[currentRow, 1].Text = currentFormula;
            sheet.Range[currentRow++, 2].Formula = currentFormula;

            MemoryStream buffer = new MemoryStream();
            workbook.SaveToStream(buffer);
            buffer.Position = 0;
            return buffer;
        }
    }
}

Imports System.IO
Imports System.Windows.Forms
Imports Spire.Xls
Module Module1

    Private Function WriteFormulas() As Stream
        Dim workbook As Workbook = New Workbook()
        Dim sheet As Worksheet = workbook.Worksheets(0)

        Dim currentRow As Integer = 1
        Dim currentFormula As String = String.Empty

        sheet.SetColumnWidth(1, 32)
        sheet.SetColumnWidth(2, 16)
        sheet.SetColumnWidth(3, 16)

        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Value = "Examples of formulas :"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Value = "Test data:"

        Dim range As CellRange = sheet.Range("A1")
        range.Style.Font.IsBold = True
        range.Style.FillPattern = ExcelPatternType.Solid
        range.Style.KnownColor = ExcelColors.LightGreen1
        range.Style.Borders(BordersLineType.EdgeBottom).LineStyle = LineStyleType.Medium

        'test data
        sheet.Range(currentRow, 2).NumberValue = 7.3
        sheet.Range(currentRow, 3).NumberValue = 5

        sheet.Range(currentRow, 4).NumberValue = 8.2
        sheet.Range(currentRow, 5).NumberValue = 4
        sheet.Range(currentRow, 6).NumberValue = 3
        sheet.Range(currentRow, 7).NumberValue = 11.3

        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Value = "Formulas"

        sheet.Range(currentRow, 2).Value = "Results"
        range = sheet.Range(currentRow, 1, currentRow, 2)
        range.Style.Font.IsBold = True
        range.Style.KnownColor = ExcelColors.LightGreen1
        range.Style.FillPattern = ExcelPatternType.Solid
        range.Style.Borders(BordersLineType.EdgeBottom).LineStyle = LineStyleType.Medium
        'str.
        currentFormula = "=""hello"""
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = "=""hello"""
        sheet.Range(currentRow, 2).Formula = currentFormula
        sheet.Range(currentRow, 3).Formula = "=""" & ChrW(20320) & ChrW(22909) + """"

        'int.
        currentFormula = "=300"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        ' float
        currentFormula = "=3389.639421"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        'bool.
        currentFormula = "=false"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=1+2+3+4+5-6-7+8-9"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=33*3/4-2+10"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula


        ' sheet reference
        currentFormula = "=Sheet1!$B$3"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        ' sheet area reference
        currentFormula = "=AVERAGE(Sheet1!$D$3:G$3)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        ' Functions
        currentFormula = "=Count(3,5,8,10,2,34)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula


        currentFormula = "=NOW()"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula
        sheet.Range(currentRow, 2).Style.NumberFormat = "yyyy-MM-DD"


        currentFormula = "=SECOND(11)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=MINUTE(12)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=MONTH(9)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=DAY(10)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=TIME(4,5,7)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=DATE(6,4,2)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=RAND()"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=HOUR(12)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=MOD(5,3)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=WEEKDAY(3)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=YEAR(23)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=NOT(true)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=OR(true)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=AND(TRUE)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=VALUE(30)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=LEN(""world"")"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=MID(""world"",4,2)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=ROUND(7,3)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=SIGN(4)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=INT(200)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=ABS(-1.21)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=LN(15)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=EXP(20)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=SQRT(40)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=PI()"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=COS(9)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=SIN(45)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=MAX(10,30)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=MIN(5,7)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=AVERAGE(12,45)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=SUM(18,29)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        currentFormula = "=IF(4,2,2)"
        currentRow = currentRow + 1
        sheet.Range(currentRow, 1).Text = currentFormula
        sheet.Range(currentRow, 2).Formula = currentFormula

        Dim buffer As New MemoryStream()
        workbook.SaveToStream(buffer)
        buffer.Position = 0

        Return buffer
    End Function
    Sub Main()
        Using buffer As Stream = WriteFormulas()
            'load
            Dim workbook As New Workbook()
            workbook.LoadFromStream(buffer)

            'calculate formula
            Dim b3 As [Object] = workbook.CaculateFormulaValue("Sheet1!$B$3")
            Dim c3 As [Object] = workbook.CaculateFormulaValue("Sheet1!$C$3")
            Dim formula As [String] = "Sheet1!$B$3 + Sheet1!$C$3"
            Dim value As [Object] = workbook.CaculateFormulaValue(formula)
            Dim message As [String] = [String].Format("Sheet1!$B$3 = {0}, Sheet1!$C$3 = {1}, {2} = {3}", b3, c3, formula, value)
            MessageBox.Show(message)
        End Using
    End Sub
End Module