http://web2.0calc.com/ - Punch in (1 << 0) and you'll receive 1, (1 << 1) to receive 2, (1 << 2) to receive 4, (1 << 3) to receive 8, etc. So 8 == FL_ONTRAIN. You can use 8, (1 << 3), or FL_ONTRAIN, they all mean the same.
PHP Code:
new iFlags = GetEntProp(client, Prop_Send, "m_fFlags");
iFlags &= ~FL_ONTRAIN; //Remove flag
if(iFlags & FL_DUCKING) //possess flag
iFlags |= FL_ONGROUND; //Add Flag.
SetEntProp(client, Prop_Send, m_fFlags, iFlags);
__________________