photoshop learning PHP learning operators and operator precedence

Arithmetic operator
Operator Name Result
$a + $b Addition The sum of $a and $b
$a - $b Subtraction The difference between $a and $b
$a* $b Multiplication Product of $a and $b
$a / $b Division quotient of $a divided by $b
$a % $b Modulo Remainder of $a divided by $b
Increment/decrement operator
Operator Name Result
++$a Add before ​$ The value of a is increased by one, and then the operation is performed
  $a++   is added after   The value of $a is operated first, and then is added by 1
 --$a   Subtract before     The value of $a is decremented by 1, and then the operation is performed
  $a--             Subtract after  $ The value of a is first operated and then reduced by one. Example:
echo $a=5+”5th”; //Output: 10
echo 10%3; //Output: 1
echo 10+ $ a++; //Output: 20
echo 5- --$a; //Output: -5
?>
Comparison Operator
Operator Name Result
$a == $b Equals TRUE if $a equals $ b
$a === $b Congruent TRUE, if $a is equal to $b, and their types are also the same
$a != $b Not equal TRUE, if $a is not equal to $b
$a <> ; $b is not equal TRUE if $a is not equal to $b
$a !== $b is not congruent TRUE if $a is not equal to $b, or they are of different types
$a < $b is less than TRUE, If $a is strictly less than $b
$a > $b is greater than TRUE, if $a is strictly $b
$a <= $b is less than or equal to TRUE, if $a is less than or equal to $b
$a >= $ b is greater than or equal to TRUE if $a is greater than or equal to $b
Another conditional operator is the " ? : " (or ternary) operator.
Example:
var_dump(0=="a"); //Output: bool(true)
var_dump(0=="00"); //Output: bool(true) var_dump(0 ==="00"); //Output: bool(false)
var_dump(0<>"abc"); //Output: bool(false)
var_dump(0!=="01"); // Output: bool(true)
$a=10;
$b=20;
$str=$a>$b? "true":"false";
echo $str; //Output: false
?>
Logic operators 算 The operator name results
$ a and $ B logic and true, if $ a and $ B are TRUE.
$a or $b Logical OR TRUE, if either $a or $b is TRUE.
$a xor $b XOR TRUE if $a and $b are different at the same time
! $a Logical NOT TRUE if $a is not TRUE.
$a && $b Logical AND TRUE, if $a and $b are both TRUE.
$a || $b Logical OR TRUE, if either $a or $b is TRUE.
Among them, and and &&, or and || are two ways of writing the same logical operator.
Logical AND and Logical OR are both short-circuit operators. When encountering the following logical expressions, the PHP interpreter will not evaluate the expression on the right:
  $a=10;
 if(false && (++$a));
 echo $a; //Output: 10
       $b=10;
                                                                                                                                                                      Set the specified bit in the number. If both left and right arguments are strings, the bitwise operators will operate on the ASCII values ​​of the characters.
Expression Name Result
The bitwise AND of $a & $b will set the bits in $a and $b that are both 1 to 1.
$a | $b Bitwise OR will set the bit that is 1 in $a or $b to 1.
$a ^ $b Bitwise XOR will set different bits in $a and $b to 1.
~ $a Bitwise NOT sets the bits in $a that are 0 to 1, and vice versa.
$a << $b Shift left Move the bit in $a to the left $b times (each move means "multiply by 2").
$a >> $b Right shift Move the bits in $a to the right $b times (each move means "divide by 2").
Other operators
String operators
There are two string operators. The first is the concatenation operator ("."), which returns the concatenated string of its left and right arguments. The second is the concatenation assignment operator (".="), which appends the right argument to the left argument.
Error suppression operator
In the most common database connection and file creation operations or when exceptions such as division by 0 occur, the @ symbol can be used to suppress the output of function error information to the browser $a=@(5/0)
External command Execute Use `` to run the external system command. Note that it is not a single quotation number, it is the key below ESC
& lt;? PHP
$ o = `dir c:`;
proprint_r ($ OUT); It is recommended to use
Example:
$a="hello";
$a.=" world! "; // Equivalent to: $a=$a." world!";
echo $a; / /Output: hello world!
$m = 3;
$m += 5; //Equivalent to: $m=$m+5;
echo $m; //Output: 8
$c = ($b = 4) + 5;
echo $c; //Output: 9
?>
Operator precedence
The following table lists the precedence of operators from low to high.
Combine direction operators
left ,
left or
left xor
left and
right print
right -= *= /= .= %= &= |= ^=                                                                       >=
LEFT ?:
LEFT ||
LEFT &&
Combined direction operator
LEFT |
LEFT ^
LEFT &
None == != === !==
None < <= > > ;=
Left                                                                                                                       .
Right [
None new
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