Can you tell me the symptoms of gangrene in a diabetic?

Pain / discoloration. Gangrene develops when the tissues die due to loss of blood flow the first sign is discoloration. The tissue first looks mottled then pale before slowly turning darker and darker until completely black. This is typically a painful process. However diabetic patients with neuropathy may have less pain.
Sure. Gangrene is basically dead tissue. There are two basic causes: lack of circulation and infection. In diabetes, both causes may be present. The gangrenous tissue itself has no sensation but the surrounding healthier tissue may become very painful. However, many diabetics have decreased sensation - and may not feel it at all. A foul smell is also common.