CWnd* pBtn5->ShowWindow(0);

void CChangeSizeView::OnButton4() 
{
	// TODO: Add your control notification handler code here
	CWnd* pBtn5= this->GetDlgItem(IDC_BUTTON5);
	pBtn5->ShowWindow(0);

}

void CChangeSizeView::OnButton6() 
{
	// TODO: Add your control notification handler code here
	CWnd* pBtn5= this->GetDlgItem(IDC_BUTTON5);
	pBtn5->ShowWindow(1);	
}