How to use the switch keyword in PHP and what to pay attention to

How to use the switch keyword in PHP and precautions

In PHP programming, switch is a commonly used conditional statement that can execute different code blocks based on different values ​​of variables. This article will introduce how to use the switch keyword and some things to pay attention to.

1. switch syntax structure:
   switch statement consists of multiple cases and a default default. Its basic syntax structure is as follows:

switch (conditional expression Formula) {

case 值1:
    代码块1;
    break;
case 值2:
    代码块2;
    break;
...
default:
    默认代码块;
    break;

}

The conditional expression can be a variable or an expression. The value after the case is compared with the value of the conditional expression. If it matches, the corresponding code block is executed. , until the break keyword or the end of the switch statement is encountered. If there is no matching value, the default code block is executed.

2. How to use switch:
   The following uses a practical example to demonstrate the use of switch.

$day = "Wednesday";

switch ($day) {

case "星期一":
    echo "今天是星期一";
    break;
case "星期二":
    echo "今天是星期二";
    break;
case "星期三":
    echo "今天是星期三";
    break;
case "星期四":
    echo "今天是星期四";
    break;
case "星期五":
    echo "今天是星期五";
    break;
default:
    echo "今天不是工作日";
    break;

}
?>

In the above code, different code blocks are executed according to different values ​​of $day, and the corresponding results are output.

3. Notes:

3.1 Value type of case: The value after case can be an integer, a string or a constant. It should be noted that the switch statement in PHP uses relaxed comparison, that is, type conversion is performed when comparing values. Therefore, if you use a string as the value of a case, you need to pay attention to whether the upper and lower case matches.

3.2 The role of break: The break keyword is used to terminate the execution of the current code block and jump out of the switch statement. If break is not used, the program will continue to execute the code block in the next case until it encounters break or ends the switch statement.

3.3 Default position: The default code block can be located anywhere in the switch statement, but usually for the readability and uniformity of the code, it is customary to place it at the end of the switch statement.

3.4 Nestable use: In case, switch statements can be nested. But please note that the nested switch statement must have its own break statement, otherwise only the current case will be jumped out, not the entire switch statement.

3.5 Scope of use: The switch statement is suitable for situations where different code blocks need to be executed based on different values. However, not all conditional judgments are suitable for using switch. For example, when a combination of multiple conditions is required, Not suitable for use with switch.

Summary:
This article introduces the usage and precautions of the switch keyword in PHP. The case demonstrates the basic syntax structure of switch and how to execute corresponding code blocks based on different conditional values. In practical applications, we need to pay attention to the value type of case, the role of break, the position of default, and precautions for nesting. Mastering the use of switch statements can make our code more concise and clear, and improve programming efficiency.

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