PHP 循环

PHP循环是一种代码，可以帮助我们在循环内部运行一些代码，根据我们的输入要求一遍又一遍地运行，这些循环将帮助我们无限地运行代码并完成任务，如下所示我们希望在循环内一次又一次地执行相同的代码，直到条件变为假，否则代码会连续运行。这个词表示只有当某个条件为真时才会重复，这在循环参数中提到，用于检查 PHP 循环的条件。

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PHP 的不同循环

与其他编程语言一样，PHP 提供了不同的循环概念。它们是：WHILE 循环、DO WHILE 循环、FOR 循环、FOREACH 循环。下面您将详细了解 PHP 的每个循环概念。

1. While 循环

只有当循环中提到的条件为真时，While 循环才会运行 PHP 的 while 循环括号内的特定/某些代码块；如果条件为 false，则 While 循环会中断代码，这是在不断运行代码的过程中。

语法：

While(Condition to check){
//Code which is need to executed or the code statements which is to run
}

说明：

在上面的语法中，在括号内提到了一个 while 循环，只有当提到的条件为 True 时才运行循环内的语句，否则循环内的代码将不会通过打破循环来运行跳出循环/while 循环。

示例：

下面的示例由 while 循环编程组成，用于打印从 1 到 10 的数字列表。在下面的示例中，变量 1 被赋值为数字 1，然后循环程序在 $i 变量的帮助下开始值和 while 循环。 while循环以条件i

代码：

<?php
$i = 1;
while($i <= 10){
echo " Now The number is " . $i . "<br>";
$i=$i+1;
}
?>

输出：

2.执行 While 循环

Do While 循环先执行循环内的编程代码，然后检查循环条件，而 While 循环则在运行循环内的代码之前检查循环条件。

语法：

do{
//Programming statements which is need to be executed only if the loop condition is true
}
While(condition to check);

示例：

下面的程序包含 2 个 do while 程序，用于打印 1-10 之间的偶数列表和 1-10 之间的奇数列表。该程序还打印奇数、偶数的总和以及 1-10 之间所有自然数的总和。第一个 do-while 循环检查变量 $i 的值，看看它是否可以被值“2”整除。如果为 True，则将打印该值，并且 $k 值将存储 $i 值；否则，什么也不会发生，只是 $i 变量值增加。

同样，循环继续，直到 $i 值达到值“10”。类似地，其他 do while 循环也通过检查 $j 值是否不会被 2 个值除来运行。如果为 True，则将打印 $j 值，并且 $m 将存储该值。最后，将偶数之和存储在变量$k中，将奇数之和存储在变量$l中。另外，将所有自然数的总和存储在变量 $m 中。在输出中显示这些值，如图所示。

代码：

<?php
$i = 1;
echo "List of Even Numbers between 1-10:: ";
$k = 0;
$m = 0;
do{
if($i%2==0){
echo " $i " ." , ";
$k=$k+$i;
}
$m=$m+$i;
$i=$i+1;
}while($i <= 10);
echo "<br>"." Sum of the total even numbers between 1-10 ::"." $k";
echo "<br>";
$j = 1;
$l = 0;
echo "List of the ODD Numbers between 1-10:: ";
do{
if($j%2!=0){
echo " $j " ." , ";
$l=$l+$j;
}
$j=$j+1;
}while($j <= 10);
echo "<br>"." Sum of the total odd numbers between 1-10 ::"." $l";
echo "<br>";
echo "<br>"." Sum of the total natural numbers between 1-10 ::"." $m";
echo "<br>";
?>

输出：

3. For 循环

For 循环在比较 While 循环和 Do While 循环时有些不同。如果满足特定条件，代码将重复执行。循环根据指定条件多次执行代码。

For 循环将有 3 个参数。它们是初始化、条件和For循环括号内的增量值。

语法：

for(initialization value; condition value; incrementing value){
//Programming code statements which is need to be executed when condition of the loop becomes TRUE
}

For 循环的参数：

• Initialization: In For Loop, this is the value/variable value to start the program.
• Condition: In For Loop, this is the value/variable value that must be checked. If the condition becomes true, then the program statements will run continuously by checking the condition.
• Incrementing/Incrementation: The program will increment the initial or running value of the program statements by 1 or another value as required, depending on our needs, in a For loop.

Example:

The below for loop example will print the list of the natural numbers between 1-30 and the sum of all the values between 1-30.

To begin, we set $i as 1 for the initial value. The condition is that $i should be less than or equal to 30, with an increment of $i+1. For loop will print the $i value until the i value becomes 30, and the $j variable’s value will store all the numbers/values of the $i variable and then sum them one by one in the loop until the I value reaches 30. After printing all the natural numbers using the For Loop, the sum of all natural numbers between 1-30 will be displayed.

Code:

<?php
echo "List of the Natural Numbers between 1-30 :: ";
$j=0;
for($i=1; $i<=30; $i++){
echo "$i" . " , ";
$j=$j+$i;
}
echo "<br>";
echo "Sum of all the natural numbers between 1-30 :: ";
echo "$j";
echo "<br>";
?>

Output:

4. Foreach Loop

PHP uses the “foreach” loop concept to iterate over arrays or multiple arrays.

Syntax:

foreach($array as $value){
//Programming code which is need to be executed
}

Example:

The below example will print the values from the $colors1 variable. $colors1 variable values are the list of the colors. Using the foreach loop concept will print the colors in the array individually.

Code:

<?php
$colors1 = array("Yellow", "Red", "Blue", "Green",);
// Colors array accessing in the loop
foreach($colors1 as $value1){
echo $value1 . "<br>";
}
?>

Output:

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