The first wxWidgets program:Hello world!

#include "wx/wx.h"
class MyApp: public wxApp
{
    virtual bool OnInit();
};
class MyFrame: public wxFrame
{
public:
    MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size);
    void OnQuit(wxCommandEvent& event);
    void OnAbout(wxCommandEvent& event);
    DECLARE_EVENT_TABLE()
};
enum
{
    ID_Quit = 1,
    ID_About,
};
BEGIN_EVENT_TABLE(MyFrame, wxFrame)
    EVT_MENU(ID_Quit,  MyFrame::OnQuit)
    EVT_MENU(ID_About, MyFrame::OnAbout)
END_EVENT_TABLE()
bool MyApp::OnInit()
{
    MyFrame *frame = new MyFrame( _("Hello World"), wxPoint(50, 50), wxSize(450, 340) );
    frame->Show(true);
    SetTopWindow(frame);
    return true;
}
MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
       : wxFrame(NULL, -1, title, pos, size)
{
    wxMenu *menuFile = new wxMenu;
    menuFile->Append( ID_About, _("&About...") );
    menuFile->AppendSeparator();
    menuFile->Append( ID_Quit, _("E&xit") );
    wxMenuBar *menuBar = new wxMenuBar;
    menuBar->Append( menuFile, _("&File") );
    SetMenuBar( menuBar );
    CreateStatusBar();
    SetStatusText( _("Welcome to wxWidgets!") );
}
void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
{
    Close(true);
}
void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
{
    wxMessageBox( _("This is a wxWidgets Hello world sample"),
                  _("About Hello World"), 
                  wxOK | wxICON_INFORMATION, this );
}
IMPLEMENT_APP(MyApp)