Control flow statement: application of if/else statement in PHP

In PHP programming, control flow statements are essential. One of the important control flow statements is the if/else statement.

if/else statements are used to execute different blocks of code based on one or more conditions. It is a conditional statement that is usually used to control the flow of a program. In PHP, the syntax structure of the if/else statement is as follows:

if (条件1) {
  //条件1成立时执行的代码块
} elseif (条件2) {
  //条件2成立时执行的代码块
} else {
  //以上条件均不成立时执行的代码块
}

In the above syntax, the execution process of the if/else statement is as follows:

• First test whether condition 1 is true, If true, execute the code block when condition 1 is true.
• If condition 1 is not true, test whether condition 2 is true. If condition 2 is true, execute the code block when condition 2 is true.
• If neither condition 1 nor condition 2 is true, execute the code in the else statement block.

The following is an example showing the application of if/else statements in PHP:

<?php
$age = 20;
if ($age < 18) {
  echo "你还未成年，不能购买此商品。";
} elseif ($age >= 18 and $age < 60) {
  echo "你可以购买此商品。";
} else {
  echo "你已经超过购买年龄，不能购买此商品。";
}
?>

Based on the above example, suppose a website wants to limit the age range for purchasing a certain product. If the age is less than 18 years old, it will prompt "You are not under age and cannot purchase this product"; if the age is between 18 and 60 years old, the product information will be displayed and the purchase will be allowed; otherwise it will prompt "You are over the purchasing age and cannot purchase this product". Buy this item".

Through this example, we can see the application scenarios of if/else statements.

In PHP, if/else statements can form complex conditions through various comparison operators and logical operators. At the same time, if/else statements can also be nested, and new if/else statements can be added to an if/else statement block.

Summary:

• The if/else statement is one of the control flow statements in PHP programming.
• If/else statements execute different blocks of code based on one or more conditions.
• if/else statements can be nested, and complex conditions can be formed through various comparison operators and logical operators.
• The application scenarios of if/else statements are very wide, such as making judgments based on user input data, performing specific operations based on the status of an event, etc.

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