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# Comparison Operators

Comparison operators, as their name implies, allow you to compare two values. You may also be interested in viewing the type comparison tables, as they show examples of various type related comparisons.

表格 15-4. Comparison Operators

Example | Name | Result
--- | --- | ---
$a == $b | Equal | `TRUE` if $a is equal to $b.
$a === $b | Identical | `TRUE` if $a is equal to $b, and they are of the same type. (introduced in PHP 4)
$a != $b | Not equal | `TRUE` if $a is not equal to $b.
$a <> $b | Not equal | `TRUE` if $a is not equal to $b.
$a !== $b | Not identical | `TRUE` if $a is not equal to $b, or they are not of the same type. (introduced in PHP 4)
$a < $b | Less than | `TRUE` if $a is strictly less than $b.
$a > $b | Greater than | `TRUE` if $a is strictly greater than $b.
$a <= $b | Less than or equal to | `TRUE` if $a is less than or equal to $b.
$a >= $b | Greater than or equal to | `TRUE` if $a is greater than or equal to $b.

If you compare an integer with a string, the string is converted to a number. If you compare two numerical strings, they are compared as integers. These rules also apply to the switch statement.

`<?php var_dump(0 == "a"); // 0 == 0 -> true var_dump("1" == "01"); // 1 == 1 -> true switch ("a") { case 0: echo "0"; break; case "a": // never reached because "a" is already matched with 0 echo "a"; break; } ?>`

See also strcasecmp(), strcmp(), Array operators, and the manual section on Types.

## Ternary Operator

Another conditional operator is the "?:" (or ternary) operator.

範例 15-2. Assigning a default value
`<?php // Example usage for: Ternary Operator $action = (empty($_POST['action'])) ? 'default' : $_POST['action']; // The above is identical to this if/else statement if (empty($_POST['action'])) { $action = 'default'; } else { $action = $_POST['action']; } ?>`

The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to `TRUE`, and expr3 if expr1 evaluates to `FALSE`.

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