Detailed explanation of "while" loop statement examples of PHP loop control statements

In our program development, sometimes we may need to repeatedly use a certain piece of code or a certain function. For example, we need to enter "1*2*3*4...*100". If it is input manually, it will It wastes a lot of time and is also very tedious. However, in this case, there is a good way to use our PHP loop control statement. Using the PHP loop control statement, the calculation can be completed quickly. In PHP, for We provide four loop control statements: while, do...while, for, and foreach. In this chapter, I will first explain to you the first type of loop control statement "while" loop statement.

The syntax format of the "while" loop statement

The while loop is the simplest loop statement in PHP

while (expr){
           statement;
}

Grammar Detailed explanation:

The structure is the same as the if statement. It also depends on a condition, but The difference is that the if statement only executes a statement when expr is true, while the while statement only executes a statement. If expr is true, the statement will be executed repeatedly. The loop will not be broken out until the value of the expression is false.

If you do not give the while condition to jump out of the loop, then the expression expr will always be true, and the loop will execute forever, which forms an infinite loop. This is our program not allowed. Think of the following code

<?php
whie(1){
    echo 1111.&#39;<br />&#39;;
}
?>

while condition is 1, which is always true, so it will keep looping, which is an infinite loop, causing the page to crash

while loop example

This example is to realize the output of even numbers within 10, and judge whether it is an even number from 1 to 10. If it is, output it. If not, Then continue the next cycle, the code is as follows

<?php
header("Content-type:text/html;charset=utf-8");    //设置编码

$num=1;                             //声明一个整型变量$sum
$str="10以内的偶数为：";            //上面一个字符串变量$str

while($num<=10){                    //判断变量$num是否小于10
    if($num%2==0){                  //如果小于10，则判断$num是否为偶数
        $str.=$num." ";              //如果变量为偶数的话，则添加到字符变量$str的后面
    }
    $num++;                         //变量$num加1
}
echo $str;                          //循环结束，输出字符串$str


?>

Code execution result:

The above is just a simple while loop example, If you want to be proficient By using the whlie loop statement in the project, you can have more experience in the actual development process in the future. In the next section, we will explain to you the "do...while" loop statement.

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