question regarding switch conditionals in php

I was hoping someone had a clue as to why I got the following outputs because I was expecting something else.

$x = NULL;
switch ($x) {
    case "0": 
        echo "String"; 
        break;
    case 0: 
        echo "Integer"; 
        break;
    case NULL: 
        echo "NULL"; 
        break;
    case FALSE: 
        echo "Boolean"; 
        break;
    case "": 
       开发者_如何转开发 echo "Empty string"; 
        break;
    default: 
        echo "Something else"; 
        break;
}
// outputs "Integer" was expecting "NULL"

$x=6;
switch ($x) {
    case "6b": 
        echo "6b"; 
        break;
    case "6": 
        echo "6 empty"; 
        break;
    case 6: 
        echo "6 full"; 
        break;
    default: 
        echo "6 half";
        break;
}
// outputs "6b" was expecting "6 empty"

The manual says:

Note that switch/case does loose comparision.

It will first check whether NULL == "0" which is false as NULL as a string is not "0".

NULL as integer is 0 so that will match - printing Integer.

For the 6, it will convert the cases to integers - "6b" will become 6 which is equal.

So it's because:

NULL != "0";
NULL == 0;

"6b" == 6;

Note:

Note that switch/case does loose comparision.

http://php.net/manual/en/control-structures.switch.php

So in stead of doing a comparison like: $x === 0 you do $x == 0

The comparison done by switch/case works with type jugling.

Basically, it uses the == operator, and not the === one.

Quoting Comparison Operators :

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically.
These rules also apply to the switch statement.

$x is automatically converted to an integer when doing the comparison "$x = 0". You might want to use an if/else if structure instead, and use $x === 0 to do the comparison. === means "strictly equal to".