3 Basic PHP syntax

Start with <?php and end with?>

Semicolon

Function Execution statement: must add a semicolon. is to add a semicolon to the code statement.

Code Structure statement: Do not add semicolons. Just like the function {} curly braces are not appended

Comments

...... Single-line Comment

/*/... * * Multi-line Comments (multiple lines of comments cannot be nested in multiple lines of comment)

#...... Script comments

/**......*/Document Comments

Note: It is often customary to write comments to the top or right of the code, i.e. write the comments before writing the code

variables

A variable is a container that is temporarily stored

PHP is a weak type of language

The variable starts with a $ symbol followed by a letter, a number, an underscore, but not a number.

<php  $a = "Hello";   $b = +;   $c =true;? >

Variable variable

$a = "Hello";

$ $a = "PHP"; Actual: $ $a is $ ($a), i.e. $hello

Note: You cannot add other characters between two $ characters and must be close to, such as $my $ A = = $myhello This does not exist

<?  $a= "Hello"; $$a= "php"; Var_dump ($a);  Hellovar_dump($$a);  PHPvar_dump($hello
?>

Ways to manipulate variables

unset () Delete variable

Isset () detects if the variable is set

Empty () detects if the variable is null

Var_dump () detects the variable type and value, which is the type and value of the input variable

<?PHP$a= "Hello"; $b=""; Var_dump($a); Var_dump($b); Var_dump(Empty($b));//$b is empty, empty ($b) returns True　　 Var_dump(isset($c));//$c Undefined, isset ($c) returns false 　　 unset($b);//delete variable?>

A reference to a variable

& Symbols

<?PHP$a=10;$b=&$a;Echo $a." </br> "; Echo $b." </br> ";//$b the same address as $ A$a=100;Echo $a." </br> ";// -Echo $b." </br> ";// -$b=200;Echo $a." </br> ";// $Echo $b." </br> ";//200

From the above can be seen, re-assign one of the values, the other changes
?>

1. Only variables have addresses

$b = &10; 10 is not a variable, error

2. One variable changes and the value of the other variable changes

3. When using unset (), if there is a referential relationship, deleting a variable simply deletes the reference relationship

4. A variable can have only one reference address, if you give it two addresses, then the following address overwrites the previous address, the reference relationship of the preceding address is broken

<?PHP//the address of a variable to two or more variables, changing one of the other full changes$a=10;$b=&$a;$c=$a; or$a=10;$b=&$a;$c=$b;//two different addresses to the same variable, after giving the overwrite first given, first give the broken reference relationship$a=10;$c=111;$b=&$a;$b=$c//b before receiving the address of a, now receive the address of C, whichever is later?>

3 Basic PHP syntax