php switch statement returns invalid output

Question

php switch statement returns invalid output :

$cond = "Night";

switch($cond){
    case "Morning":
    case "Night":
        $name = "Good";

    case "Morning" :
        echo $name." Morning";
        break;

    case "Night" :
        echo $name." Night";
        break;
}

output : Good Morning

Expected Good Night

Edit (after reading replies) :

Thanks for answers. I didn't get a clear answer.

I know i can use another statement like if else. But logically the code should work correctly(I think). because there's no break after 2 first cases .

but why when execution reaches to case "Morning" , the condition is true while isn't true in real?

There is not a break after the second case, so it will go through the next case, and there's a break on the next case, once your code sees the break, it'll exit from switch-case. — Firat Akandere
– Firat Akandere, Commented Jan 10, 2016 at 10:15
you said : ` and there's a break on the next case` this break shouldn't work if the case condition isn't true. — AliN11
– AliN11, Commented Jan 10, 2016 at 10:55
PHP doesn't evaluate any other case conditions once it has found a true one. It blindly continues executing statements falling through the cases until it finds a break. — trincot
– trincot, Commented Jan 10, 2016 at 11:28

Professor Abronsius · Accepted Answer · 2016-01-10 10:15:30Z

2

You could do it slightly differently - as there is always going to be a good you could do this:

$cond = "Night";
$pre='Good ';

switch($cond){
    case "Morning" : echo $pre." Morning"; break;
    case "Night" : echo $pre." Night"; break;
}

answered Jan 10, 2016 at 10:15

Professor Abronsius

33.9k5 gold badges36 silver badges49 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

AliN11 Over a year ago

There are another cases . i created first case because the Morning and Night have similar conditions.

u_mulder · Accepted Answer · 2016-01-10 10:15:04Z

1

As you didn't add break first case - execution continues and breaks after

echo $name." Morning";

But even if you add break statement for the first case - you won't reach last case:

case "Night" :
    echo $name." Night";
    break;

as execution already out of switch-block.

So you have to write some other code with another logic. Simple one is:

$cond = "Night";

switch($cond){
    case "Morning":
    case "Night":
        echo "Good" . $cond;
        break;
}

answered Jan 10, 2016 at 10:15

u_mulder

54.8k5 gold badges54 silver badges72 bronze badges

Comments

trincot · Accepted Answer · 2016-01-10 11:23:10Z

0

The switch construct is always a bit of a risk when you do not specify a break, as execution will just continue to the next cases without testing those conditions.

As stated in the docs, I emphasise in bold:

It is important to understand how the switch statement is executed in order to avoid mistakes. The switch statement executes line by line (actually, statement by statement). In the beginning, no code is executed. Only when a case statement is found with a value that matches the value of the switch expression does PHP begin to execute the statements. PHP continues to execute the statements until the end of the switch block, or the first time it sees a break statement. If you don't write a break statement at the end of a case's statement list, PHP will go on executing the statements of the following case.

So, to be clear: PHP does not verify case conditions any more once it has started executing statements inside a case. Without a break, it will just continue with the statements of the next cases without verifying the case conditions. And so it goes from case to case, executing all statements until it finds a break or the end of the switch.

So the following code:

switch (1) {
case 1:
    echo "one ";
case 2:
    echo "two ";
case "hello":
    echo "hello ";
}

will output:

one two hello

PHP finds the first case condition to be true and starts executing statements without evaluating any other case conditions.

This may be very counter-intuitive, and also makes the code less readable. It is best practice to put a break at the end of each case to avoid any misunderstanding.

edited Jan 10, 2016 at 11:23

answered Jan 10, 2016 at 10:54

trincot

357k38 gold badges282 silver badges339 bronze badges

2 Comments

AliN11 Over a year ago

Thanks. but why PHP considers case "Morning"(3rd case) as true ? while isn't true.

trincot Over a year ago

It doesn't consider it as true, like it says in the docs, it just executes the statements without verifying anything until the next break. This is what I mean "risky" to use. But it is the same in other languages as well.

Marcin Nabiałek · Accepted Answer · 2016-01-10 10:24:33Z

It seems the order here is important, if you used:

$cond = "Night";

switch($cond){
    case "Morning":
    case "Night":
        $name = "Good";

    case "Night" :
        echo $name." Night";
        break;        

    case "Morning" :
        echo $name." Morning";
        break;
}

you would get what you expect. However as you see it can't be easily predicted what would be exact result, so depending on your needs, I would do it in different way, for example I would use 2 switches for that:

$cond = "Night";
$name = '';
switch($cond){
    case "Morning":
    case "Night":
        $name = "Good";
        break;
}

switch ($cond) {
    case "Morning" :
        echo $name." Morning";
        break;    
    case "Night" :
        echo $name." Night";
        break;
}

or even simpler:

$cond = "Night";
$name = '';
switch($cond){
    case "Morning":
    case "Night":
        $name = "Good";
        break;
}

switch ($cond) {
    case "Morning" :
    case "Night" :
        echo $name." ".$cond;
        break;
}

Now everything will be obvious and noone will have difficulty to understand what's going on here.

RST · Accepted Answer · 2016-01-10 10:31:00Z

0

To keep things organized you could do something like this. You will not need the switch

$cond = "Night";
$name = array (
     'Morning' => 'Good',
     'Night' => 'Good'
     );
echo $name[ $cond ]." ".$cond;

In this case you don't have to add another switch case for new situations, just add an entry to the $name array

answered Jan 10, 2016 at 10:31

RST

3,9252 gold badges24 silver badges33 bronze badges

2 Comments

AliN11 Over a year ago

I know i can do that using another statement like if and else if

RST Over a year ago

If/else is not the same. But if the other way fits your logic better than that is okay. Just try to use every code only once, instead of with every case or every if/else. You will be happy for it when you want to change something. Using it the way I suggested is also faster, there is no checking involved.

Yuri Blanc · Accepted Answer · 2016-01-10 10:53:32Z

0

If you don't break; your switch it will continue and step into next cases.

    $cond = "Night";

switch($cond){
    case "Morning":
    case "Night":
        $name = "Good";
        break; // add this

    case "Morning" :
        echo $name." Morning";
        break;

    case "Night" :
        echo $name." Night";
        break;
}

this happens also with other languages such as java, is called fall through

answered Jan 10, 2016 at 10:53

Yuri Blanc

64510 silver badges25 bronze badges

Comments

Jakir Hossain · Accepted Answer · 2016-01-10 10:33:26Z

-1

Try this code.

$cond = "Night";
$name = "Good ";
switch($cond){
    case "Morning":
        echo $name . $cond;
    break;
    case "Night":
        echo $name . $cond;
    break;
}

edited Jan 10, 2016 at 10:33

answered Jan 10, 2016 at 10:24

Jakir Hossain

2,51720 silver badges24 bronze badges

Collectives™ on Stack Overflow

php switch statement returns invalid output

7 Answers 7

1 Comment

Comments

2 Comments

Comments

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

1 Comment

Comments

2 Comments

Comments

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related