for (int i = 0; i < clbIncludes.Items.Count; i++)
if (clbIncludes.GetItemChecked(i))
// Do selected stuff
else
// Do unselected stuff
If the the check is in indeterminate state, this will still return true. You may want to replace
if (clbIncludes.GetItemChecked(i))
with
if (clbIncludes.GetItemCheckState(i) == CheckState.Checked)
if you want to only include actually checked items.