How does php output different results by judging conditions?

In PHP development, we often need to output different content or execute different logic based on specific conditions or situations. At this time, we need to use PHP's if statement to output different results by judging conditions.

The basic usage of the if statement is to first specify a condition, and then decide whether to execute a specific code block based on the condition. The basic syntax of the if statement is as follows:

if (条件) {
    //代码块
}

Among them, "condition" specifies the condition for judgment. If the condition is met, the content in the "code block" will be executed. If the condition is not met, the code block will be skipped directly and subsequent code execution will continue.

In actual development, we can write different judgment conditions and code blocks according to specific business needs. Let’s introduce some common judgment logic and code implementation.

1. Determine whether a variable exists or is empty

In PHP, we can use the isset() and empty() functions to determine whether a variable exists or is empty. . Among them, the isset() function is used to determine whether the variable exists, and the empty() function is used to determine whether the variable is empty. If the variable exists and is not empty, the return values ​​​​of the isset() and empty() functions are true; otherwise, it returns false. Therefore, we can implement the above judgment logic through the following code block:

if (isset($var)) { //判断变量是否存在
    //代码块1
}

if (!empty($var)) { //判断变量是否非空
    //代码块2
}

2. Judge the size of the value

In PHP, we can use comparison operators to compare the size of the value . Comparison operators include:

• Greater than (>)
• Less than (<)
• Greater than or equal to (>=)
• Less than Equal to (<=)
• Equal to (==)
• Not equal to (!=)

Therefore, we can implement the numerical size through the following code block Judgment logic:

if ($num > 10) { //判断$num是否大于10
    //代码块1
}

if ($num <= 100) { //判断$num是否小于等于100
    //代码块2
}

3. Judge string content

In PHP, we can use string functions to judge the content of a string. The more commonly used string functions include:

• strpos(): Determine whether the string contains a certain substring. If it does, return the position of the substring in the string, otherwise return false.
• strlen(): Get the length of the string.
• strncmp(): Compare the first N characters of the string to see if they are equal.
• preg_match(): Use regular expressions to match strings.

Therefore, we can implement the judgment logic of string content through the following code block:

if (strpos($str, "PHP") !== false) { //判断$str中是否包含PHP
    //代码块1
}

if (strlen($str) > 10) { //判断$str的长度是否大于10
    //代码块2
}

if (strncmp($str1, $str2, 3) === 0) { //判断$str1和$str2的前3个字符是否相等
    //代码块3
}

if (preg_match('/^[\w\-]+@[\w\-]+(\.[\w\-]+)+$/', $email)) { //使用正则表达式判断$email格式是否正确
    //代码块4
}<ol start="4"><li>Multiple judgment logic</li></ol>
<p>In actual development , we may need to judge multiple conditions at the same time, in which case we need to use multiple judgment logic. PHP supports the following multiple multiple judgment logics: </p>
<ul>
<li>Logical AND (&&): Only when multiple conditions are met, the corresponding code block will be executed. </li>
<li>Logical OR (||): As long as one condition is met, the corresponding code block will be executed. </li>
<li>Logical NOT (!): negation operation, that is, if the condition is not true, the corresponding code block is executed. </li>
</ul>
<p> Therefore, we can implement multiple judgment logic through the following code block: </p>
<pre class="brush:php;toolbar:false">if ($num > 10 && $num <= 100) { //判断$num是否大于10并且小于等于100
    //代码块1
}

if ($str1 === "hello" || $str2 === "world") { //判断$str1是否等于hello或者$str2是否等于world
    //代码块2
}

if (!(isset($var1) && empty($var2))) { //判断$var1是否存在或者$var2是否为空
    //代码块3
}

Summary

PHP’s if statement can help us determine and output different content based on conditions Or perform different logic. In actual development, we will encounter various business needs, so we need to be proficient in using if statements to write precise judgment logic and code implementation. At the same time, we also need to pay attention to the readability and maintainability of the code to avoid lengthy, complex logic and repeated code.

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