IF-ELSE 和 SWITCH 有什么区别? [英] What is the difference between IF-ELSE and SWITCH?

问题描述

有人可以向我解释一下吗?

Can someone please explain this to me?

推荐答案

它们非常相似，但都有一些特殊功能.

They are pretty similar but each has a few special features.

切换

• switch 通常比许多嵌套的 if else 更紧凑，因此更具可读性
• 如果您省略两个 switch case 之间的 break，在许多类 C 语言中，您可能会遇到下一个 case.使用 if else 你需要一个 goto(这对你的读者来说不是很好......如果语言完全支持 goto).
• 在大多数语言中，switch 只接受原始类型作为键和常量作为大小写.这意味着编译器可以使用非常快的跳转表对其进行优化.

• 如何正确格式化switch并不是很清楚.从语义上讲，案例是跳转目标(如 goto 的标签)，应该向左对齐.当你有花括号时，事情会变得更糟:

• switch is usually more compact than lots of nested if else and therefore, more readable
• If you omit the break between two switch cases, you can fall through to the next case in many C-like languages. With if else you'd need a goto (which is not very nice to your readers ... if the language supports goto at all).
• In most languages, switch only accepts primitive types as key and constants as cases. This means it can be optimized by the compiler using a jump table which is very fast.

• It is not really clear how to format switch correctly. Semantically, the cases are jump targets (like labels for goto) which should be flush left. Things get worse when you have curly braces:

case XXX: {
} break;

或者大括号应该单独成行吗?右大括号应该放在 break 后面吗?那会有多难读?等

Or should the braces go into lines of their own? Should the closing brace go behind the break? How unreadable would that be? etc.

if-else

• if 允许条件中的复杂表达式而 switch 需要一个常量
• 您不会不小心忘记了 if 之间的 break，但您可以忘记 else(尤其是在剪切和粘贴期间)
• 它接受所有数据类型.

• if allows complex expressions in the condition while switch wants a constant
• You can't accidentally forget the break between ifs but you can forget the else (especially during cut'n'paste)
• it accepts all data types.

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