in case的用法，归纳起来，主要有以下三种：

■ 用作连词，表示条件，其意为“如果”“万一”。如：

In case you see him, ask him about it. 如果你见着他，问问他这事。

Tell me in case you get into difficulty. 遇到困难请告诉我。

If case I forget, please remind me about it. 万一我忘记，请请醒我一下。

■ 用作连词，表示目的，其意为“以防”“免得”。如：

I’ll take my raincoat in case it rains. 我将带上雨衣，以防下雨。

I shall sit up for a time, in case I’m wanted. 我暂时不睡以防需要我。

I bought the car at once in case he changed his mind. 我马上买下了那辆汽车，以免他变卦。

I don’t let him climb trees in case he tears his trousers.  我不让他爬树，以免撕破裤子。

■ 起副词作用，其意为“以防万一”。如：

You’d better carry some money in case. 你最好带些钱，以防万一。

The sun is shining, but I’ll take an umbrella just in case. 现在是晴天，但我还是带上雨伞以防万一。

The dog was chained, but I carried a stick in case. 狗是用链条锁住的，但我带着一根棍子以防万一。