如果R中的语句只能有一行？ [英] if statement in R can only have one line?

问题描述

我正在使用if语句尝试一个很小的代码，虽然它非常简单，但我在这里真的很困惑的是代码

I was trying a tiny code with if statement, although it is very simple,but there is something I really confused here is the code

n<-857
while(n!=1){
if(n<=0)
 print("please input a positive integer")
else if(n%%2==0)
 n<-n/2
 print(n)
else
 n<-3*n+1
 print(n)
  }

如上所述，在R中运行此代码时，出现错误，但是如果我更改if语句就像这样

as we see above,when running this code in R, there comes the error,but if I change the if statement like this

if(n<=0)
     print("please input a positive integer")
    else if(n%%2==0)
     n<-n/2
    else
     n<-3*n+1

没关系，我的问题是我们每次判断只能写一行吗？如果我想在每个评判后做更多的事情，我该怎么办，就像这个案例一样，我想改变n的值，但也想要显示它，我该怎么办？非常感谢

it is ok ,my question is that can we only write one line under each judgement? if I want to do something more after each judge, what should I do ,just like this case, I want to change the value of n,but also want to display it, what should I do? thank you very much

推荐答案

确切地说，这不是关于行而是关于语句。您可以在一行中包含整个 if else 语句：

To be precise, this is not about lines but about statements. You can have the whole if else statement in one line:

> if (TRUE) 1 else 3
[1] 1

声明将在行的结尾（如果完成），如果你逐行输入代码，你可以很好地在交互模式中看到：

A statement will end at the end of the line (if complete), you can see that nicely in interactive mode if you enter the code line by line:

> if (TRUE) 
+ 1
[1] 1
> else
Fehler: Unerwartete(s) 'else' in "else" # error: unexpected 'else' in "else"
> 3
[1] 3

if 可以以形式出现if（条件）语句或 if（condition）语句else else.statement ，解释器假设第一个版本意味着如果语句在第2行之后完成 - 在交互模式下它无法明智地等待接下来是否出现 else 。这在 source d代码中是不同的 - 在下一行中它是明确的形式。

if can come in form if (condition) statement or if (condition) statement else other.statement, the interpreter assumes the first version is meant if the statement is complete after line 2 - in interactive mode it cannot sensibly wait whether an else appears next. This is different in sourced code - there it is clear with the next line which form it is.

分号结束语句：

> if (TRUE) 1; else 3
[1] 1
Fehler: Unerwartete(s) 'else' in " else"  # error: unexpected 'else' in "else"

但在条件的每个分支中只能有一个语句。

But you can only have one statement in each branch of the condition.

> if (TRUE) 1; 2 else 3
[1] 1
Fehler: Unerwartete(s) 'else' in " 2 else" # error: unexpected 'else' in "2 else"

卷曲括号组语句，使它们显示为一个语句。

Curly braces group statements so they appear as one statement.

> if (TRUE) {1; 2} else 3
[1] 2

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