Detailed explanation of PHP{} block-level scope

This article mainly shares with you {} block-level scope and and && or || priority issues, I hope it can help everyone.

and && or || Priority issue:

and or has a lower priority than && || and lower than =.
Therefore $b1 = $bA and $bBThe first operation is $b1 = $bA.

$bA = true;$bB = false;$b1 = $bA and $bB;$b2 = $bA && $bB;
var_dump($b1); // $b1 = truevar_dump($b2); // $b2 = false$bA = false;$bB = true;$b3 = $bA or $bB;$b4 = $bA || $bB;
var_dump($b3); // $b3 = falsevar_dump($b4); // $b4 = true

{}Block-level scope:

In php, the internal value can be obtained outside {}. PHP has function scope, but not block scope.

if(1){    $a = 123;
}
print_r($a);  // $a = 123;

for ($i = 0; $i < 10; $i++) {    for ($j = 0; $j < 10; $j++) {        $k = 777;
    }
}
var_dump($j);//输出10var_dump($k);//输出777

$arr = [1, 2, 4];foreach ($arr as &$val) {    $val  *= 2;
}$val = [];//重新赋值$val[0]=9;$val[1]=10;
var_dump($arr,$val);

输出：array(3) {
  [0]=>
  int(2)
  [1]=>
  int(4)
  [2]=>
  &array(2) {
    [0]=>
    int(9)
    [1]=>
    int(10)
  }
}array(2) {
  [0]=>
  int(9)
  [1]=>
  int(10)
}

Since $arr ​​as &$val, loop to the third element,

val. Although it is reassigned to an empty array, subsequent modifications will still affect

val is a reference, and subsequent modifications will affect it. , unless unset($val) is added.

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