PHP Loops - While Loops

PHP Loops

When you write code, you often need to run the same block of code over and over again. Instead of adding several nearly equal lines of code to the script, we can use a loop to perform such a task.

In PHP, we have the following loop statement:

· while - As long as the specified condition is true, the loop code block

· do...while - execute the code block once first, and then repeat the loop as long as the specified condition is true

· for - loop the code block a specified number of times

· foreach - traverse the array each element in and loop the code block

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##PHP while loop

while is a Boolean loop. If the value of while (Boolean judgment) is true, the code enclosed in curly brackets will be executed. If it is false, stop and execute the subsequent code.

grammar

while (condition is true){

//Executed code;

}

Example

The following example first sets the variable $x is 1 ($x=1). The while loop is then executed as long as $x is less than or equal to 5. Each time the loop runs, $x will increase by 1:

<?php
 header("Content-type:text/html;charset=utf-8");    //设置编码
 $x=1;
 while($x<=5){
     echo "这个数是---".$x ."<br/>";
     $x++;
 }
 ?>

Look at the results of the program:

This number is---1

This The number is---2
The number is---3
The number is---4
The number is---5

Note: Do not write an infinite loop (a loop without exit conditions) like the following program

<?php

whie(1){
echo 1111.'<br / >';
}?>

while condition is one, which is always true, so it will keep looping, which is a loop, causing the page to crash

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##PHP do...while Loop

do...The difference between while and while is that their values ​​are checked at different times.

do-while Regardless of whether the while judgment is true, the code block loop statement is executed once, and it is guaranteed to be executed once (the truth value of the expression is checked after each loop).

However, our while loop above will check the Boolean judgment area and execute it if it is true. If not established, it will not be executed.

Syntax

##do{

//Executed code ;

}while (condition is true);

---

Example

The following example first sets the variable $x to 1 ($x=1). Then, the do while loop outputs a string and then increments the variable $x by 1. The condition is then checked (whether $x is less than or equal to 5). As long as $x is less than or equal to 5, the loop will continue to run. Anyway, the loop ends

<?php
 header("Content-type:text/html;charset=utf-8");    //设置编码
 $x=1;
 do {
     echo "这个数字是：$x <br>";
     $x++;
 } while ($x<=5);
 ?>

Let's take a look

do...while condition is not The running result of the program when it is satisfied:

<?php
 header("Content-type:text/html;charset=utf-8");    //设置编码
 $x=6;
 do {
     echo "这个数字是：$x <br>";
     $x++;
 } while ($x<=5);
 ?>

The above example fully illustrates that even if the conditions of the do...while loop are not satisfied, the code will Execute it once

The for loop and foreach loop will be explained in the next chapter.