+2  A: 

From winuser.h:

#define CBS_DROPDOWN          0x0002L
#define CBS_DROPDOWNLIST      0x0003L

You need:

switch(m_MyComboBox.GetStyle() & CBS_DROPDOWNLIST)
{
  case CBS_SIMPLE:
    // do stuff
    break;

  case CBS_DROPDOWN:
    // do stuff
    break;

  case CBS_DROPDOWNLIST:
    // do stuff
    break;
}
Serge - appTranslator
Ok, this was indeed what I needed to get further but... Actually ((m_MyCoboBox.GetStyle() -)
fretje
Ok, thanks for clarifying the answer (I've seen that you updated it to also reflect what Shino answered). Because you were first I'm accepting yours as the right answer (I upvoted Shino's because he was the first to give a more complete answer)
fretje
+3  A: 

Use following code

if ((m_MyComboBox.GetStyle() & 3) == CBS_SIMPLE)
{
 //SIMPLE
}
if ((m_MyComboBox.GetStyle() & 3) == CBS_DROPDOWN)
{
 //DROPDOWN
}
if ((m_MyComboBox.GetStyle() & 3) == CBS_DROPDOWNLIST)
{
 //DROPDOWNLIST
}
Shino C G