CODEWITHSUNDEEP
cgcc
Piotr
Piotr

Reputation: 41

If ... else switch ... statement

Following code compiles on my gcc 5.4.0, doesn't generate any warnings and works fine:

if (a == 0) {
    puts("0");
} else switch (a) {
    case 1: puts("1"); break;
    case 2: puts("2"); break;
    default: puts("default"); break;
}

Is if ... else switch ... correct statement?

Upvotes: 3

Views: 1869

Answers (5)

Attie
Attie

Reputation: 6969

What you have is syntactically correct... but it does not make easy reading.

You will likely be pulled up on it if your code is being reviewed - because you're making use of an "un-braced, multi-line statement as part of a conditional".

Prefer to be explicit and write it like so:

if (a == 0) {
    puts("0");
} else {
    switch (a) {
        case 1: puts("1"); break;
        case 2: puts("2"); break;
        default: puts("default"); break;
    }
}

It is legal in the same way that the following is legal:

if (a == 0)
    puts("0");
else
    puts("not0");

Such constructs can lead to mistakes when re-visiting the code... I seem to remember that one of the recent "popular" vulnerabilities was implemented (by mistake... hopefully) in part due to this "un-braced" use of if.

Upvotes: 4

magicleon94
magicleon94

Reputation: 5162

Nothing wrong with your code, that is the same of writing this:

if (a == 0) {
    puts("0");
} else {
    switch (a) {
        case 1: puts("1"); break;
        case 2: puts("2"); break;
        default: puts("default"); break;
    }
}

That is perfectly legit. else switch is not a real statement.

Your statement is 

if(condition){code block} else {code block}

code block can contain any statement, such as your switch statement.

Upvotes: 3

Mohit Jain
Mohit Jain

Reputation: 30489

Syntax of if is:

if ( condition ) statement-true  else statement-false
condition is an expression convertible to a boolean (true/false)
statement-true is a statement which is executed if condition is true
statement-false is a statement which is executed if condition is false

And switch block is a statement.

So yes, your code exhibit correct statement.

Upvotes: 2

unwind
unwind

Reputation: 399703

The switch is a statement, so this is just putting a statement in the else.

It's no different from

else
  a = 0;

or

else
{
  switch(a)
  {
  case 1:
  ...
  }
}

It's not a very common way of writing it, but it's fine.

Upvotes: 3

Vittorio Romeo
Vittorio Romeo

Reputation: 93264

There's nothing wrong with your code. The grammar for if ... else is as follows:

attr(optional) if ( condition ) statement-true else statement-false

switch is a statement, so it is allowed to go after else.

Note that else if is not a special construct either, it's just an if statement after an else.

Upvotes: 9

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