if statement in R can only have one line?

Question

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) } ``` 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 ``` 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

Accepted Answer

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
```

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` 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 `source`d code - there it is clear with the next line which form it is.

Semicolons end statements as well:

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

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"
```

Curly braces group statements so they appear as one statement.

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

if statement in R can only have one line?

Solution

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