What loop structures are there in PHP?

The loop structures in PHP are for loop, while loop, do-while loop and foreach loop. Detailed introduction: 1. for loop, the initialization expression is used to initialize the value of the loop control variable, the conditional expression is used to determine whether the loop continues to execute, and the increment expression is used to control the change of the loop control variable; 2. while loop, the conditional expression is used To determine whether the loop continues to execute; 3. do-while loop, first execute the loop body code once, and then determine the conditional expression; 4. foreach loop, etc.

The operating environment of this article: Windows 10 system, php8.1.3 version, dell g3 computer.

PHP is a popular server-side programming language that provides a variety of looping structures that allow developers to handle repetitive tasks easily. In PHP, there are four common loop structures, namely for loop, while loop, do-while loop and foreach loop. The usage and characteristics of these loop structures will be introduced one by one below.

1. The for loop is one of the most commonly used loop structures. Its syntax is as follows:

for (初始化表达式; 条件表达式; 递增表达式) {
// 循环体代码
}

In the for loop, the initialization expression is used to initialize the value of the loop control variable, the conditional expression is used to determine whether the loop continues to execute, and the increment expression is used to control the loop. Changes in control variables. During each loop iteration, the loop body code will be executed once. For example, the following is an example of calculating the sum of numbers from 1 to 10:

$sum = 0;
for ($i = 1; $i <= 10; $i++) {
$sum += $i;
}
echo $sum; // 输出55

2. The while loop is another commonly used loop structure. Its syntax is as follows:

while (条件表达式) {
// 循环体代码
}

In the while loop, the conditional expression is used to determine whether the loop continues to execute. The loop body code will be executed only when the conditional expression is true. For example, the following is an example of a guessing number game:

$number = rand(1, 10); // 生成一个1到10之间的随机数
$guess = 0;
while ($guess != $number) {
$guess = readline("请输入你猜的数字：");
if ($guess < $number) {
echo "太小了！";
} elseif ($guess > $number) {
echo "太大了！";
} else {
echo "猜对了！";
}
}

3. The third loop structure is the do-while loop. Its syntax is as follows:

do {
// 循环体代码
} while (条件表达式);

The difference between do-while loop and while loop is that do-while loop will first execute the loop body code once, and then judge the conditional expression. If the conditional expression is true, the loop body code will continue to be executed; otherwise, the loop ends. For example, the following is an example of a simple counter:

$count = 0;
do {
echo $count;
$count++;
} while ($count <= 10);

4. The foreach loop is a loop structure used to traverse an array. Its syntax is as follows:

foreach (数组 as $值) {
// 循环体代码
}

In the foreach loop, the array is the array to be traversed, and the $ value is the variable of the array element. During each loop iteration, the $ value will take each element of the array in turn. value of elements. For example, the following is an example of traversing an array and outputting the array elements:

$fruits = array("苹果", "香蕉", "橙子");
foreach ($fruits as $fruit) {
echo $fruit;
}

Summary

PHP provides for loops, while loops, do-while loops and foreach loops There are four common loop structures. Developers can choose the appropriate loop structure to handle repetitive tasks according to different needs. Proficient in the usage and characteristics of these loop structures can improve the efficiency and readability of the program, thereby better completing programming tasks

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