How to get the scroll bar in ccombobox

You need to increase the height of the drop down of combo box in designer.

Through the designer by default you can just resize the ComboBox width. If you want to resize the Drop Down List height you need to click on the dropdown arrow on the right, then you'll be able to resize the dropped control height. This seems so easy but if no-one tells you it's anything but intuitive.

Another method to set height of the drop down of combo box is to manualy edit rc file. You can set 5th parameter which is responsible for height of the drop down (72 in this example).

COMBOBOX IDC_COMBOBOX1,17,35,157,72,CBS_DROPDOWN | CBS_SORT | WS_VSCROLL | WS_TABSTOP