How to add items to ComboBox in MFC?

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C++

MFC

i created a dialog based MFC app

there i added a combobox

i assigned a variable to combobox using wizard as combobox1

using add handler wizard, i added OnCreate Routine to the dialogbox file

when i add items to combobox in that routine, it compiles successfully but its creating problem at runtime, saying "Debug Assertion Failed" and pointing to some internal library..

i used the code

int CSampleMFCDlgDlg::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    if (CDialogEx::OnCreate(lpCreateStruct) == -1)
        return -1;

    combobox1.AddString(L"Hello");
    combobox1.AddString(L"World");

    return 0;
}

whats wrong with it??