in case用作连词时有以下两个用法：

1. 表示条件，意为“如果”“万一”。如：

In case it rains, do not expect me. 如果下雨，就不要等我了。

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

In case I forget, please remind me of my promise. 如果我忘了，请提醒我我的诺言。

In case he arrives before I get back, please ask him to wait. 如果他在我回来之前到，请让他等等我。

2. 表示目的，意为“以防”“生怕”。如：

I’m shy of buying shares in case I lose money. 我不敢买股票，怕赔钱。

Take warm clothes in case the weather is cold. 带些暖和的衣服，以防天气变冷。

I’ll keep a seat for you in case you should change your mind. 我给你留一个座位，以防你会改变主意。

We took our swimming things in case we happened to find a pool. 我们带上游泳用品，以备万一能找到一个水池。

注：有时中间的谓语由 should构成，强调偶然性，可译为“万一”：

I wrote down her address in case I should forget it. 我写下了她的地址，以防万一我忘了。

I always slept by the phone in case he should ring during the night. 我总是睡在电话机旁边，怕万一他夜间打电话来。