while（$ variable）在PHP中意味着什么？

Question

I am new to PHP and am currently constructing a do/while loop from a tutorial. I would understand if the whole condition was ($variable == true) or ($variable == false), however in the tutorial the while condition is simply while($variable). Could anyone explain this to me?

Here is the tutorial code.

<?php
    $loopCond = false;
    do {
        echo "<p>The loop ran even though the loop condition is false.</p>";
    } while ($loopCond);


    echo "<p>Now the loop is done running.</p>";
?>

Answer 1

All such conditional statements, including while and if, are evaluating the given expression against true. If the expression results in true, the statement executes the action. If it results in false, it won't.

$var == true is an expression which compares $var to true. The result of this expression is either true or false. The important point to understand here is expressions. Expressions are things which return values. Try var_dump($var == true) or var_dump(4 > 6). It shows you that the expressions return a boolean value. Here:

if ($var == true)

first $var is compared to true, which yields either the value true or false, which is then evaluated by if whether it's true or false, which then prompts if to execute the following statement or not.

In other words: it's redundant.

if ($var)

This simply causes if to evaluate whether $var is true or false and then execute the following statement. The == true is essentially already "built in".

The following statements are all essentially equivalent:

if ($var)
if ($var == true)
if (($var == true) == true)
if ((($var == true)) == true) == true)
...