In-depth analysis of if judgment statements in php

In PHP, the if statement is a very commonly used and important statement, used for conditional judgment and process control. It can perform branch control based on specified conditions during code execution to achieve different logical results. The main function of the if statement is to execute the specified code block when certain conditions are met. The following is a detailed introduction to the if judgment statement in PHP.

1. Basic if statement

The basic if statement is the simplest statement, consisting of the if keyword and the conditions that need to be judged. The syntax is as follows:

if (条件)
{
    // 执行这里的代码块
}

Here, the condition of the if statement is a Boolean expression that needs to be judged. If the condition is true, the code block in the curly braces will be executed. Otherwise, the code block will be skipped and the subsequent code will continue to be executed.

2. if-else statement

The if-else statement adds an else keyword to the basic if statement, in the following form:

if (条件)
{
    // 条件为真时执行这里的代码
}
else
{
    // 条件为假时执行这里的代码
}

It means: if the condition is true, execute the if code block, otherwise execute the else code block. As you can see, the if statement has only one condition, but the else statement is optional and can be written or not.

3. if-else if- else statement

if-else The if-else statement adds one or more elseif statements based on the if-else statement. , the form is as follows:

if (条件1)
{
    // 条件1为真时执行这里的代码
}
elseif (条件2)
{
    // 条件2为真时执行这里的代码
}
elseif (条件3)
{
    // 条件3为真时执行这里的代码
}
else
{
    // 以上条件都不为真时执行这里的代码
}

Its meaning is: if condition 1 is true, execute the if code block, otherwise determine whether condition 2 is true, if so, execute the elseif code block, otherwise determine condition 3. If condition 3 is true, the elseif code block is executed, if all conditions are not true, the else code block is executed.

It is worth noting that the condition in elseif is not necessary, and the condition can also be omitted, like the following:

if (条件1)
{
    // 条件1为真时执行这里的代码
}
elseif
{
    // 上一个条件为假且没有条件时执行这里的代码
}

Such a statement is equivalent to:

if (条件1)
{
    // 条件1为真时执行这里的代码
}
else
{
    // 上一个条件为假且没有条件时执行这里的代码
}

4. Special if statement writing methods

When using if statements, there are some special writing methods that can be used to simplify the code. For example:

1. How to write the ternary operator

The if statement and the ternary operator are equivalent, you can write it like this:

$foo = (条件) ? '真' : '假';

It's The meaning is: if the condition is true, the value of variable $foo is 'true', otherwise the value of variable $foo is 'false'.

2. How to write the null merge operator

After PHP7, a new operator was also introduced: the null merge operator??, which can be used to simplify if statements Writing method.

$foo = $a ?? $b;

It means: If the variable $a exists and is not null, assign the value of $a to $foo, otherwise assign the value of $b to $foo.

Summary

The above is the complete writing method of if judgment in PHP. Different writing methods have different uses and application scenarios. Programmers can use it according to the specific situation. Choose appropriate syntax. At the same time, when writing if statements, pay attention to the standardization and readability of the code to facilitate reading and maintenance by yourself and other personnel.

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