error C2679: binary '+' no operator found which takes a right-hand operand of type 'const cha

void CExampleViewView::OnInitialUpdate()
{
CView::OnInitialUpdate();

// TODO: Add your specialized code here and/or call the base class
CRect rcClient;
GetClientRect(rcClient);
if(m_ctrlEdit) delete m_ctrlEdit;

m_ctrlEdit = new CEdit();
m_ctrlEdit ->Create(ES_MULTILINE|WS_CHILD|WS_VISIBLE|WS_HSCROLL|ES_AUTOHSCROLL|WS_VSCROLL|ES_AUTOVSCROLL,rcClient, this, 201);
CExampleViewDoc* pDoc = GetDocument();
CString str;
int nLines = (int)pDoc->m_strContent.GetSize();
for(int i=0;i<nLines; i++)
{
str = str + pDoc->m_strContent.GetAt(i);
str = str + "\r\n";
}
m_ctrlEdit->SetTabStops(16);
m_ctrlEdit->SetWindowText(str);
}

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