对于Case的多个条件，Switch Statement无法正常工作

$letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']; 
$x = (1==1 || 2==2);
$y = (3==3 || 4==4);
$z = (5==5);

foreach ($letters as $key => $letter) {
        switch ($letter) {
            case 'a':
                echo "a";
                    break;
            case 'b':
                echo "b";
                    break;
            case 'c':
                echo "c";
                    break;
            case 'd':
                echo "d";
                    break;
            case 'e':
                echo "e";
                    break;
            case 'f':
                echo "f";
                    break;
            case 'g' && ($z || $y):
                echo "g";
                    break;
            case 'h' && ($x):
                echo "h";
                    break;
        }
}

I don't know why but at the last two cases the 'g' and 'h' It doesn't work properly and gets a double 'g', The result i expect is

abcdefgh but i keep getting abcdefgg, What am I doing wrong?

Given your code, the g case will always evaluate to true:

var_dump('g' && ((5==5) || (3==3 || 4==4))); // true

switch cases use loose comparison and when $letter is g it will be evaluated with true. Since g is loosley true it will execute that case:

var_dump('g' == true);  // true
var_dump('g' == false); // false

You probably need this:

        case 'g':
            if(($z || $y)) { echo "g"; }
                break;

It may be intuitive to try and assume switch will spit out boolean values, and you can then append additional boolean logic to your cases. This is wrong, however.

From the PHP docs on switch:

This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure.

Each of your cases needs to exactly match the evaluated `$letter$ expression, you cannot have additional boolean expressions and whatever else in the cases.