Controlling Flow in Your PHP Code: Loops, Conditions, and Functions

Flow control in PHP involves loops, conditions, and functions. Loops allow iterating over data (for loop, while loop, foreach loop). Conditional structures (if-else statements) execute different blocks of code based on conditions. Functions encapsulate reusable code blocks to improve code reusability and maintainability. These concepts can be used to develop complex applications, such as managing online store inventory, where an inventory array is compared with user input to determine whether an order can be fulfilled.

Controlling the flow of your code in PHP: Loops, Conditionals and Functions

Controlling the flow of your code in PHP is crucial. It allows you to execute different blocks of code based on conditions and organize your code to improve maintainability and readability. This article will delve into the use of loops, conditions, and functions, and provide practical examples to deepen understanding.

Loop: Traverse data

A loop is a structure that repeats a block of code a specific number of times or when a condition is true. PHP provides the following types of loops:

• for Loops: Allows you to iterate over a known range of times using initial values, conditions, and increments.
• while Loop: A block of code is executed indefinitely as long as a given condition is true.
• foreach Loop: Iterate over an array or object and execute a block of code for each element of it.

// 用 for 循环计算 1 到 10 的总和
$total = 0;
for ($i = 1; $i <= 10; $i++) {
    $total += $i;
}

Conditional: Selective Code Execution

The conditional structure allows you to execute different blocks of code based on a certain condition. The most common conditional structure in PHP is the if-else statement:

// 检查用户是否已登录
if (isset($_SESSION['user'])) {
    // 如果已登录，显示欢迎消息
    echo "欢迎回来，" . $_SESSION['user'];
} else {
    // 如果未登录，显示登录表单
    echo "请登录";
}

Function: Reusing code

A function is to encapsulate a set of related code into a repeatable Blocks in the module used. Doing so improves reusability, maintainability, and code clarity.

// 计算两个数字的平均值
function average($num1, $num2) {
    return ($num1 + $num2) / 2;
}

Practical Case

Now let us illustrate these concepts through a practical case. Suppose we want to create a simple PHP program to manage the inventory of an online store.

<?php

// 定义库存数组
$inventory = ['apple' => 10, 'orange' => 5, 'banana' => 15];

// 获取用户输入的水果和数量
$fruit = $_GET['fruit'];
$quantity = $_GET['quantity'];

// 检查库存
if (isset($inventory[$fruit])) {
    // 如果库存中存在该水果
    if ($inventory[$fruit] >= $quantity) {
        // 如果库存足够
        $inventory[$fruit] -= $quantity;
        echo "您成功购买了 $quantity 个 $fruit";
    } else {
        // 如果库存不足
        echo "抱歉，我们只有 {$inventory[$fruit]} 个 $fruit";
    }
} else {
    // 如果库存中不存在该水果
    echo "抱歉，我们没有 $fruit";
}

?>

In this case, we use the if-else condition to check the inventory and execute different code depending on whether the inventory is enough. Additionally, the foreach loop is used to iterate through the inventory and find a specific fruit.

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