In case” and “if”
“In case” 和“if”

Consider this sentence:
看一下下面的句子:

In case it rains I will take an umbrella.
以防下雨,我要带把雨伞。

This means : Because there is a possibility that it will rain later, I will take an umbrella now.
这句话的意思是:因为一会儿有下雨的可能,我现在要带把雨伞。

“In case…” is an idiomatic phrase that we use when we talk about taking precautions.
“In case”为习语性词组,通常在要采取预防措施的情况下使用。

It is used mainly in informal speaking and writing.
主要用于非正式口语和写作中。

“Just in case…” is a version of the phrase commonly used in spoken language:
“just in case(以防万一)”是这个词组的变形,通常用于口语当中。

“I’ll pack an extra shirt, just in case.”
“我还是再装件衬衫吧,以防万一。”

“In case…” DOES NOT mean “if…”
“In case” 不等于“if”

Now consider this sentence:
现在看一下下面的句子:

If it rains I will take an umbrella.
如果下雨,我就带把雨伞。

This means the following: If it is raining at the moment I leave the house, I will take an umbrella, but if it is not raining, I won’t.
这句话的意思是:如果我离开家的时候下雨,我就带把雨伞,但如果不下雨,我就不带了。

In the case that it rains I will take an umbrella.
如果下雨,我就带把雨伞。

means the same thing.
这句话的意思和上面是一样的。

“If …” = “In the case that…” / “in the event that…”
“If” 等于“In the case that”或者“in the event that”

Compare the following sentences:
对比下面的句子:

In case my house is burgled I’ll take out insurance.
=> as a precaution BEFORE it is burgled
以防家里被盗,我要买一份保险。
=> 作为一种预防,发生在被盗之前。

If my house is burgled I’ll take out insurance.
=> AFTER it has been burgled? That’s too late!
如果我的家被盗,我要买一份保险。
=> 发生在被盗之后?太晚了吧!

In case I crash the car I’ll wear a seatbelt.
=> as a precaution BEFORE I have a crash
为了防止撞车,我要要系上安全带。
=> 作为一种预防,发生在撞车之前。

If I crash the car I’ll wear a seatbelt.
=> AFTER you have crashed? That’s too late!
如果我撞车了,我会系上安全带。
=> 发生在自己撞车之后?太晚了!

“In the case of…”
“In the case of” 就...而言

“In the case of…” means “as regards” / “with regard to” / “as far as … is concerned” etc. For example:
“In the case of”等于 “as regards (至于)”/ “with regard to(就...而言)”/ “as far as...is concerned ( 据...考虑)”等等,例如:

In the case of the Property, the lease agreement has been executed for a period of ten years.
至于所有权的问题,该借贷协议已经执行了10年。

(As regards the Property…)
(至于所有权问题......)

“In the case of…” can also mean “for”, as in this example:
“In the case of…” 也可以表示“for(因为)”例如:

The authority may impose a fine in the case of non-compliance with the regulations.
如果企业违反该条例,政府可以进行罚款。

(…for non-compliance)
(......因为违反......)

“In case of…” (without “the”)
“In case of... ”(没有“the”)

“In case of…” (without “the”) means “in the case that” / “if”. It is used exclusively in formal notices and announcements.
“In case of...”(没有 the)指的是“in the case that (如果)”/ “if (如果)”。该词只在正式的通知和宣告中。

For example:
例如:

In case of fire do not use the lift.
如果发生火灾,不要使用电梯。

(If there is a fire…)
(如果发生火灾......)

In case of rain the wedding reception will be held in the hotel ballroom.
如果下雨,婚礼接待就在酒店的舞厅举行。

(If it rains…)
(如果下雨......)

“In case of…” (without “the”) SHOULD NOT be used except in formal notices and announcements.
“In case of ...”(没有 the)仅用于正式的通知和宣告中。