CODEWITHSUNDEEP
phpconditional-statements
nanopart
nanopart

Reputation: 98

PHP switch and if statement output different results

Could someone please explain what's going on here? Here's the code:

$num = 0;

switch($num){

case ($num==0):
    echo $num ,  " is ZERO";
    break;

case ($num>0):
    echo $num ,  " is POSITIVE";
    break;

default:echo $num , " is NEGATIVE";
}

The above outputs 0 is POSITIVE

if($num==0){

print ($num." is ZERO");

} 

elseif($num>0){

echo $num ,  " is POSITIVE";

}

else{

echo $num , " is NEGATIVE";

}

This works as expected - 0 is ZERO. If I replace case($num==0) with case(0) the output is OK.

Why does the case($num==0) fail? Someone told me the issue with evaluating multiple expressions in the case statements, but it seems fine syntactically.

Upvotes: 0

Views: 118

Answers (2)

user4035
user4035

Reputation: 23719

The logical structure of switch operator is this:

switch($x):
case val1:
    action 1;
    break;

case val2:
    action 2;
    break;

default:
    not val1 and val2;

switch compares $x with one of the values or gives default branch in case nothing matches. So, you can't write:

case ($num > 0):

or

case ($num == 0 ):

In your case it gives POSITIVE, because php first evaluates the expressions inside cases, and we get the following in the output:

Is $num == 0 ?: yes => 1
Is $num > 0 ?: no => 0

And the real switch php evaluates is this:

$num = 0;

switch($num){

case 1:
    echo $num ,  " is ZERO";
    break;

case 0:
    echo $num ,  " is POSITIVE";
    break;

default:
    echo $num , " is NEGATIVE";
}

Output is: POSITIVE.

Upvotes: 1

deceze
deceze

Reputation: 521995

switch compares everything in the switch (...) expression to each case:

switch ($num) {
    case 0 :
        ...
    case 1 :
        ...
    ...
}

You don't write case $num == 0, as that's equivalent to if ($num == 0 == $num).

If at all, you'd have to do:

switch (true) {
    case $num == 0 :
        ...
    case $num > 0 :
        ...
    ...
}

But there are people who frown upon that.

Upvotes: 1

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