is switch case without break a bad practice?

Question

I have a switch in which I check a property of some sort and if the check yields a specific value, I want to check another value, so I did something like this:

switch(property_A)
{
case NA:
    if(value_0 == property_B)
        property_A = value_a;
    else if(value_1 == property_B)
        property_A = value_b;
case value_0:
...
break;
case value_1:
...
break;
}

So, I know this solves my problem, but I don't know if this is a good idea or maybe should I go about this another way

# the NA case is something like a default case but not exactly, because it does tell me something, but not enough

If you are trying to jump to the correct case after preforming what's in `NA`, it won't work. — StoryTeller - Unslander Monica, Dec 01 '16 at 14:15
It's common to allow a case to "fall through" to the next case. However, what you're doing does not "check another value". If you modify the value being switched on and want to run the `switch` from the start you need a loop. — Some programmer dude, Dec 01 '16 at 14:15
Do you want the code in `case value_o` to execute if you hit the `case NA` ? — nos, Dec 01 '16 at 14:15
wihtout break I just go to the next case, no matter what my property_A value is? — CIsForCookies, Dec 01 '16 at 14:18
Yes. That's what "fall through" means, the code will just continue. It "falls through" the bottom of the current `case` and continues with the next one below it. — Some programmer dude, Dec 01 '16 at 14:18
can I make the code go back to the switch and pick the new case WO a loop or a second switch? — CIsForCookies, Dec 01 '16 at 14:20

score 4 · Accepted Answer · edited May 23 '17 at 11:46

It depends on what you want to do. If you get to the case NA, without the break keyword, the value_0 case will be executed after one of the two if branches is finished. So if that's the behaviour you want, it's OK not to use break, but I don't think that's what you wanted to do.

I suggest you simply move the if - else statement above the switch and remove the NA case. This way, you will first assign the correct data to property_A and then you can do whatever you want with it in the switch.

EDIT: As Jack Deeth points out, if you omitted the break statement on purpose, it's a good idea to add a comment that you did so.

Jack Deeth · Answer 2 · 2016-12-06T11:53:50.640

3

Convention is to add a comment explicitly telling future-you and any other maintainers you intended the fallthough and you haven't accidentally omitted the break;.

switch(foo) {
case 1:
  bar();
  // fallthrough
case 2:
  baz();
  break;
case 3:
  fizzbuzz();
}

If you're using C++17 or later you can use the [[fallthrough]] attribute to avoid a compiler warning:

switch(foo) {
case 1:
  bar();
  [[fallthrough]]
case 2:
  baz();
  break;
case 3:
  fizzbuzz();
}

edited Dec 06 '16 at 11:53

answered Dec 01 '16 at 14:31

Jack Deeth

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2

I indeed added a comment, but wanted to know if it is a bad practice even with a comment – CIsForCookies Dec 01 '16 at 14:33

score 2 · Answer 3 · answered Dec 01 '16 at 14:52

The additional information provided in the comments to the question indicate that what's wanted is not what's written in the question:

switch(property_A)
{
  case NA:
    if(value_0 == property_B)
        property_A = value_a;
    else if(value_1 == property_B)
        property_A = value_b;
    // here, we fallthrough into the code for value_0
    // but you want to switch on the new value instead
  case value_0:
    ...
    break;
}

What you say you actually want is to set property_A if it was initially NA, then jump to the correct label. In that case, you'll need the assignment to be outside of the switch statement. You could do this with a goto at the end of the NA case, but I recommend you just deal with the NA before the switch:

if (property_A==NA)
    property_A = (value_0 == property_B) ? value_a
               : (value_1 == property_B) ? value_b
               : NA;

switch (property_A) {
  case value_0:
    ...
    break;
  case NA:
    // we get here only if none of the replacement conditions
    // matched, outside the 'case'
}

is switch case without break a bad practice?

3 Answers3

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