Definition of variables
⚑Type of variable
⚑Variable usage
Variables are objects that can be constantly changing in memory. We can imagine memory as a street. There are many residents in the street, and each resident will have his own house number. This is like an address in memory (a concept often mentioned in C language, which we will not discuss here). For one of the residents, we can say it is No. 1 Building 1, or it can also be said to be Wang Xiaoming's house, using a name instead of an address. At some point, there were a few people in Wang Xiaoming’s family. There may be 3 people at noon, only 1 person in the afternoon, and 5 people at night. Therefore, we need to refer to a certain address in memory, which can also be called A or area. This is the variable.
Let’s demonstrate the declaration of variables in PHP.
Just add a variable name with "$", such as $a, $var_name.
Note 3 points when declaring variables in PHP:
, variable names can only be composed of English letters (A-Z, a-z), numbers (0-9) and underscores.
, in PHP, variable names are case sensitive, that is, $VAR_NAME and $var_name are two different variables.
, a variable declaration or assignment must end with a semicolon (;).
The types of variables in PHP are very simple. Generally speaking, there is no need to declare them with keywords, but just use assignments to express them.
For example, declare an integer variable
$x=100;
Declare a character variable
$str=”Iam a Chinese!”;
Declare a boolean variable
$bool=true;
Use variables in web pages.
For example, we want to display a sentence on the web page, "I am a Chinese", "I am 28 years old this year."
Line 1 "<?php", which is a marker for the start of a PHP file, indicating that it is PHP code from now on.
Line 2 $str="I am a Chinese"; defines a string variable str whose value is "I am a Chinese".
Line 3 $age=28;, define an integer variable age and assign it a value of 28.
Line 4 echo$str."<br>";, echo is the keyword used to output in PHP. The content followed by it indicates that it is the content that needs to be output, that is, $str is the variable that needs to be output, and the . after $str is a tag used to connect multiple variables or variables with general content. After $str is indicated here, a newline symbol will be displayed.
Line 5 echo "I'm this year".$age." This sentence is understood in the same way as line 4. The sentence "I am 28 years old this year" is divided into three parts. "I am this year" is the first part, 28 is replaced by the variable $age, and "Age" is the third part, and they are connected by .
Line 6 "?>" means that this PHP file is over.
At this point, mission 1 is over. Until now, you can express what you want to say on the web page in PHP.
⚑Type of variable
⚑Variable usage
Variables are objects that can be constantly changing in memory. We can imagine memory as a street. There are many residents in the street, and each resident will have his own house number. This is like an address in memory (a concept often mentioned in C language, which we will not discuss here). For one of the residents, we can say it is No. 1 Building 1, or it can also be said to be Wang Xiaoming's house, using a name instead of an address. At some point, there were a few people in Wang Xiaoming’s family. There may be 3 people at noon, only 1 person in the afternoon, and 5 people at night. Therefore, we need to refer to a certain address in memory, which can also be called A or area. This is the variable.
Let’s demonstrate the declaration of variables in PHP.
Just add a variable name with "$", such as $a, $var_name.
Note 3 points when declaring variables in PHP:
, variable names can only be composed of English letters (A-Z, a-z), numbers (0-9) and underscores.
, in PHP, variable names are case sensitive, that is, $VAR_NAME and $var_name are two different variables.
, a variable declaration or assignment must end with a semicolon (;).
The types of variables in PHP are very simple. Generally speaking, there is no need to declare them with keywords, but just use assignments to express them.
For example, declare an integer variable
$x=100;
Declare a character variable
$str=”Iam a Chinese!”;
Declare a boolean variable
$bool=true;
Use variables in web pages.
For example, we want to display a sentence on the web page, "I am a Chinese", "I am 28 years old this year."
Copy the codeThe code is as follows:
<?php
$str="I am a Chinese";
$age=28;
echo$str."<br>";
echo "I'm this year".$age." It's oldest;
?>
$str="I am a Chinese";
$age=28;
echo$str."<br>";
echo "I'm this year".$age." It's oldest;
?>
Line 1 "<?php", which is a marker for the start of a PHP file, indicating that it is PHP code from now on.
Line 2 $str="I am a Chinese"; defines a string variable str whose value is "I am a Chinese".
Line 3 $age=28;, define an integer variable age and assign it a value of 28.
Line 4 echo$str."<br>";, echo is the keyword used to output in PHP. The content followed by it indicates that it is the content that needs to be output, that is, $str is the variable that needs to be output, and the . after $str is a tag used to connect multiple variables or variables with general content. After $str is indicated here, a newline symbol will be displayed.
Line 5 echo "I'm this year".$age." This sentence is understood in the same way as line 4. The sentence "I am 28 years old this year" is divided into three parts. "I am this year" is the first part, 28 is replaced by the variable $age, and "Age" is the third part, and they are connected by .
Line 6 "?>" means that this PHP file is over.
At this point, mission 1 is over. Until now, you can express what you want to say on the web page in PHP.