What is the difference between & and && in PHP

In PHP, the & operator is a bitwise AND operator, while the && operator is a logical AND operator.

The bitwise AND operator performs a bit-level AND operation on two operands. It compares each bit of the first operand to the corresponding bit of the second operand and returns a new value where each bit is set to 1 if both corresponding bits are 1, and 0 otherwise.

The logical AND operator returns true if both operands are truthy, and false otherwise.

Here are a few examples to illustrate the difference between the two operators:

$a = 5; // 0101 in binary
$b = 3; // 0011 in binary
echo $a & $b; // Outputs: 1 (0001 in binary)
echo $a && $b; // Outputs: 1

$c = 0;
$d = 1;
echo $c & $d; // Outputs: 0
echo $c && $d; // Outputs: 

In general, you should use the logical AND operator (&&) to test for boolean conditions, and the bitwise AND operator (&) to perform bit-level operations. However, it is important to note that the logical AND operator has a higher precedence than the bitwise AND operator, so you may need to use parentheses to specify the order of evaluation in some cases.

For example:

$a = 5;
$b = 3;
if ($a & $b == 1) {
  // This condition will always be true, because the bitwise AND operation is performed first
}

if (($a & $b) == 1) {
  // This condition will be true only if the result of the bitwise AND operation is 1
}