C++ uncorrect not required re-declaring of class member variable MFC handmade solution/project MS VS 2015

Question

I tried to shorten a foreign code. I thougth I could save one variable.

The following given code is OK and shows a Windows Frame.

#include <afxwin.h> 
// from source: http://www.codersource.net/2010/01/30/mfc-tutorial-part-1/
class MFC_Tutorial_Window :public CFrameWnd
{
public:
    MFC_Tutorial_Window()    
    {
        Create(NULL, "MFC Tutorial Part 1 CoderSource Window");  
    }
};

class MyApp :public CWinApp
{
    MFC_Tutorial_Window *wnd;  

public:
    BOOL InitInstance()
    {
        wnd = new MFC_Tutorial_Window();
        m_pMainWnd = wnd;                        
        m_pMainWnd->ShowWindow(1);
        return 1;
    }
};

MyApp theApp;

After my rewording it doesn`t function anymore. No build errors. But it doesn't show a frame.

#include <afxwin.h> 
// from source: http://www.codersource.net/2010/01/30/mfc-tutorial-part-1/
// and changed by me

class MFC_Tutorial_Window :public CFrameWnd
{
public:
    MFC_Tutorial_Window()
    {
        Create(NULL, "MFC Tutorial Part 1 CoderSource Window");
    }
};

class MyApp :public CWinApp
{
    // del MFC_Tutorial_Window *wnd;
    MFC_Tutorial_Window *m_pMainWnd; // ins 


public:
    BOOL InitInstance()
    {
        // del wnd = new MFC_Tutorial_Window();
        // del m_pMainWnd = wnd;
        m_pMainWnd = new MFC_Tutorial_Window(); // ins
        m_pMainWnd->ShowWindow(1);
        return 1;
    }
};

MyApp theApp;

What's the matter?

Answer 1

The problem is in redeclaration of member variable MFC_Tutorial_Window *m_pMainWnd;, without this row it'll work.