If your OnBnClickedButton1() look like
void CMultilineView::OnBnClickedButton1()
{
CString str1, str2, str3;
GetDlgItem(IDC_EDIT1)->GetWindowText(str1);
CMatrix a(str1);
GetDlgItem(IDC_EDIT2)->GetWindowText(str2);
CMatrix b(str2);
CMatrix c( a.Add(b) ); // c = a + b
Matrix2String(c, str3);
GetDlgItem(IDC_EDIT3)->SetWindowText( str3 );
}
you should be able to perform the following matrix addition