How to figure out PHP's While loop and do-while loop, five minutes is enough!

In the previous article, I brought you "How to sort PHP arrays (detailed pictures and texts)". This article introduces in detail how to sort PHP arrays. , this article continues to bring you the basic knowledge related to PHP, about PHP’s While loop. I hope to be helpful.

PHP Loop-While Loop

First of all, why does a loop exist? Why does the code use loops? In our daily use, we will encounter the need to run the same code block repeatedly. Instead of adding several nearly equal lines of code, which would be bloated, we can use a loop to perform such a task.

• What is a While Loop?

While loop is a type of PHP loop. while is a Boolean loop. It will first determine that the value of while (Boolean judgment) is true (true) and then execute the Code enclosed in parentheses. If it is false, go out and execute the following code.

• While syntax format is as follows:

while (条件) {
    动作;
}

while The calculation result of "condition" in the loop must be Boolean True (TRUE) or false (FALSE), if it is a value of other types, will also be automatically converted to a Boolean type value.

For example:

<?php
    $a = 1;
    //While循环提供条件,$a<=6时，表达式为真，会循环下去
    while($a <= 6) {
        echo "循环结果：".$a."<br/>";
        //每循环一次，通过运算符，它的值就+1
        $a++;
    }
?>

Output result:

It can be seen from the results that only when the While loop condition is calculated The While loop will stop only when the result is false.

PHP do...while loop

We have almost understood the While loop just now, let’s continue to take a look at the do...while loop.

• What is a do...while loop?

They are very similar. Let’s first look at the difference between the two: The expression of the do while loop is not checked at the beginning of each loop, but at the beginning of each loop. Check at the end.

do-while Regardless of whether the while judgment is true or not, first execute the code block loop statement once to ensure that it will be executed once, and then judge again.

• do...while loop syntax is as follows:

do {
    动作;
} while (条件);

The calculation result of the "condition" in the while statement It must also be Boolean true (TRUE) or false (FALSE).

When using do while, there must be a semicolon at the end;.

<?php
 $a=1;
 //和while循环不同的是，do-while会先执行一次动作，再去判断
 do {
     echo "循环结果是：$a <br>";
     //每循环一次，通过运算符，它的值+1
     $a++;
 } while ($a<=5);
 ?>

Output result:

<img src="/static/imghwm/default1.png" data-src="https://img.php.cn/upload/image/266/658/577/1634205480732917.png?x-oss-process=image/resize,p_40" class="lazy" title="1634205480732917.png" alt="How to figure out PHPs While loop and do-while loop, five minutes is enough!">

You can try it and assign $a to false at the beginning , that is, the do-while condition is not met. Let’s take a look at the changes in the output result:

<?php
 $a=100;
 //和while循环不同的是，do-while会先执行一次动作，再去判断
 do {
     echo "循环结果是：$a <br>";
     //每循环一次，通过运算符，它的值+1
     $a++;
 } while ($a<=5);
 ?>

Output result:

<img src="/static/imghwm/default1.png" data-src="https://img.php.cn/upload/image/453/911/484/1634205658816970.png?x-oss-process=image/resize,p_40" class="lazy" title="1634205658816970.png" alt="How to figure out PHPs While loop and do-while loop, five minutes is enough!">

Since the judgment is false, the do-while loop will not start, and the action block will only be executed once.

To summarize:

The process of do while loop is: first execute the action in the loop body once, and then judge the value of the conditional expression. When the value of the condition is input When it is TRUE, return and re-execute the action statement in the loop body, and so on until the value of the expression is equal to FALSE, and the loop ends.

Recommended learning: "PHP Video Tutorial"

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