How to add formulas in cells in C++.NET

/*----------------------------------------------------------------
 | Tutorial 11
 |
 | This tutorial shows how to create an Excel file in C++.NET that
 | has a cell that contains SUM formula for a range of cells.
 ---------------------------------------------------------------*/

#using <mscorlib.dll>

using namespace System;
using namespace EasyXLS;

int main()
{
    Console::WriteLine("Tutorial 11\n----------\n");

    // Create an instance of the class that exports Excel files
    ExcelDocument ^workbook = gcnew ExcelDocument();

    // Create a sheet
    workbook->easy_addWorksheet("Formula");

    // Get the table of data for the sheet, add data in sheet and the formula
    ExcelWorksheet ^xlsFirstTab = safe_cast<ExcelWorksheet^>(workbook->easy_getSheet("Formula"));
    ExcelTable ^xlsTable = xlsFirstTab->easy_getExcelTable();
    xlsTable->easy_getCell("A1")->setValue("1");
    xlsTable->easy_getCell("A2")->setValue("2");
    xlsTable->easy_getCell("A3")->setValue("3");
    xlsTable->easy_getCell("A4")->setValue("4");
    xlsTable->easy_getCell("A6")->setValue("=SUM(A1:A4)");

    // Export Excel file
    Console::WriteLine("Writing file C:\\Samples\\Tutorial11 - formulas in Excel.xlsx.");
    workbook->easy_WriteXLSXFile("C:\\Samples\\Tutorial11 - formulas in Excel.xlsx");

    // Confirm export of Excel file
    String ^sError = workbook->easy_getError();
    if (sError->Equals(""))
        Console::Write("\nFile successfully created. Press Enter to Exit...");
    else
        Console::Write(String::Concat("\nError encountered: ", sError, "\nPress Enter to Exit..."));

    // Dispose memory
    delete workbook;

    Console::ReadLine();

    return 0;
}