How to define PHP variables_PHP tutorial

Definition of variables
⚑Types of variables
⚑Uses of variables
Variables are objects that exist in memory and can change continuously. We can imagine the memory as a street, with many residents in the street. Each resident will have his own house number, which is like an address in memory (a concept often mentioned in C language, we will not discuss it here). For one of the residents, we can say that it is Building 1 No. 1 can also be said to be Wang Xiaoming's home, using a name instead of an address. The number of people in Wang Xiaoming's family at a given time is a variable quantity. There may be 3 people at noon, only 1 person in the afternoon, and 5 people at night. Therefore, if we want to refer to a certain address in the memory, we can also call it A, or area. This is the variable.
Let’s demonstrate the declaration of variables in PHP.
Just use "$" to add a variable name, such as $a, $var_name.
Note three points when declaring variables in PHP:
. Variable names can only consist of English letters (A-Z, a-z), numbers (0-9) and underscores.
. Variable names in PHP 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 type specification of variables in PHP is very simple. Generally, there is no need to declare it with keywords, and it can be reflected in the form of assignment.
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 code The code is as follows:

$str="I am a Chinese";
$age=28;
echo$str."
";
echo"I am this year".$age."years old";
?>

Line 1 " Line 2 $str="I am a Chinese"; defines a string variable str, whose value is "I am a Chinese".
Line 3 $age=28; defines an integer variable age and assigns it a value of 28.
Line 4 echo$str."
";, echo is the keyword used for output in PHP, and the content following it indicates the content that needs to be output, that is, $str is the variable that needs to be output. , and the . after $str is a mark used to connect multiple variables or variables with general content. Here, it indicates that a newline symbol
will be displayed after $str.
Line 5 echo "I am this year".$age."years old";, 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. "Age" is the third part. They are connected by .
Line 6 "?>" indicates the end of this PHP file.
At this point, mission 1 is over. Up to now, you can express what you want to say on the web page in the form of PHP.

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