Thread: Class problem in C++

Code:

#include <afxwin.h>
#include "Resource.h"

class DialogApp : public CWinApp
{
public:
	BOOL InitInstance();	
};

class CExoDialog : public CDialog
{
public:
	enum { IDD = IDD_DIALOG1 };

	CExoDialog();
};

CExoDialog::CExoDialog()
	: CDialog(CExoDialog::IDD, NULL)
{
}

BOOL DialogApp::InitInstance()
{	
	CExoDialog Dlg;
	m_pMainWnd = &Dlg;
	Dlg.DoModal();

	return TRUE;
};

DialogApp theApp;

//End of test31.CPP

I don't understand meaning of the following code. Please give some explain. Thanks indeed.

Code:

CExoDialog::CExoDialog()
	: CDialog(CExoDialog::IDD, NULL)
{
}