Master PHP's if else syntax and NULL data type in 5 minutes

In the previous article, I brought you "An exciting and easy-to-remember summary of PHP variable knowledge (details)". This article continues to bring you an explanation and introduction of PHP knowledge. Let’s take a look at the common if else syntax and NULL data type in PHP. They are all basic knowledge. I hope it can help everyone!

if-else syntax in PHP

if and else syntax is an important syntax in PHP. It is recommended that everyone must master the if statement proficiently. It is the simplest type of process control. Only determine whether a certain condition is true, and if it is true, execute a specific statement block.

if and else syntax have four basic syntaxes:

• if statement: when the condition is true (also is a single line of code that is executed when the condition is true). Code examples are as follows:

<?php
if(布尔条件)
   布尔值为真(true)时执行的代码;
?>

In actual use, we often have more than one code to execute. At this time, a simple code cannot satisfy us. When writing multiple lines of code, we only need Use braces {} to wrap the code to represent a whole; if there is only one statement to be executed, you can omit the brace mark. Then you can extend another basic syntax:

• Multiple lines of code that are executed when the condition is true (that is, when the condition is true).

<?php
if(布尔条件){
    布尔值为真(true)时执行，可写多行代码;
}
?>

• if...else statement, in actual use, it is not enough to have only one condition true, so There is also an if else statement, which can not only determine whether the condition is true, but also determine whether the condition is false. A single line of code that is executed when the condition is true (that is, when the condition is true), and another single line of code that is executed when the condition is not true (that is, when the condition is false). The code example is as follows:

<?php
if(布尔条件)
   布尔值为真(true)时执行的代码;
else
   布尔值为假(false)时执行的代码;
?>

• Multiple lines of code executed when the condition is true (that is, when the condition is true).

<?php
if(布尔条件){
    布尔值为真(true)时执行，可写多行代码;
}
?>

• if...else statement - multiple lines of code that are executed when the condition is true (that is, when the condition is true), and when the condition is not true (that is, the condition is false) another multiple lines of code executed.

<?php
if(布尔条件){
    布尔值为真(true)时执行，可写多行代码;
}else{
   布尔值为假(false)时执行，可写多行代码;
}
?>

Then actually put together, the example is as follows:

The variable assignment is true, so the code when the condition is true is output in the if conditional statement, also That is: study hard and make progress every day.

<?php
//定义一个变量为真（true），也就是布尔值为true
$a = true;
//运行if条件
if($a){
    //变量为真则输出：好好学习天天向上
    echo &#39;好好学习&#39;;
    echo &#39;天天向上&#39;;
}else{
    //变量为假则输出：福如东海寿比南山
    echo &#39;福如东海&#39;;
    echo &#39;寿比南山&#39;;
}
?>

Output result:

php data type null type

NULL is a type in PHP A special data type that has only one value, NULL, which represents a null value (the variable has no value) and does not represent spaces.

When the following conditions are met, the value of the variable is NULL:

• The variable is assigned a NULL value;

<?php
//声明变量为null，变量被指定为NULL
$a = null;
var_dump($a);
?>

Output result:

• Before a variable is assigned a value, the default value is NULL;

<?php
//var_dump显示输出变量$a，但$a未被赋值。
var_dump($a);
?>

Output result:

• After using the unset() function to delete a variable, this variable The value is also NULL.

<?php
//声明一个变量$a
$a = &#39;好好学习&#39;;
//unset销毁掉一个变量unset($a),这个变量值也为NULL
var_dump($a);
?>

Output result:

Related to NULL Two functions: empty() and isset()

• empty() A variable is passed in the brackets. If the value of the variable is false or null, it is passed out. is true. An example is as follows:

<?php
//给变量赋值为null，也可以试试flase。
$a = null;
//运行if和empty
if(empty($a)){
//empty传出的是true
    echo &#39;好好学习&#39;;
}else{
//empty传出的不是true
   echo &#39;天天向上&#39;;
   }
?>

Output result:

It can be seen that the variable a is passed as null through empty() out true.

• #isset() Pass one or more variables between the brackets, and separate variables with commas. As long as there is a variable that is null, it returns false. Otherwise, returns true. For example:

One variable:

<?php
//一个变量为null，
$a = null;
$b = isset($a);
var_dump($b);
?>

The output result is:

Multiple variables :

<?php
//多个变量赋值
$a = 1;
$b = false;
$c = 0;
$d = null;
//运行isset，多个变量，其中有一个null
$all = isset($a , $b , $c , $d);
var_dump($all);
?>

The output result is:

It can be seen that through isset(), multiple variables with nulls in them are passed to flase .

Recommended learning: "PHP Video Tutorial"

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