PHP basic syntax

One 、 initial PHP Script program

1.PHP Language marks
    1)PHP Start marker ：<?php
    2)PHP End mark ：?>
    3) Our page is finally through html,css,js To show a gorgeous interface
    4)PHP Code can be embedded in html Anywhere in the code , And can embed any number of
    5) The end of the file "?>" The end flag can be omitted
2 . Instruction separator ";"
    1) In some PHP Add... At the end of the statement ";" It means the end of a sentence , Of course, you don't need to miss the semicolon , The program can't be executed at all , Will report a mistake .
    2) End mark "?>" It implies a “;” So in "?>" Previous PHP Statements can be omitted ";"
3. notes
     1) Multiline comment
             /* Things that need annotation */
     2) Single-line comments
             // Things that need annotation
 

Two 、 Variable （ A container for temporarily storing data ）

1、 Declaration of variables

       C Language must define variables at the beginning of the code , Is a declaration , And in the PHP In the program , Variables do not need to be declared before they are used .（“=” stay php It also means assignment ）

2. Destruction of variables
unset ($ Variable name ）
3. Naming rules for variables
      1) Variable names are strictly capitalized
              $name, $NANE, $Name It's all different variables
       2) Only start with letters or underscores

    * Variable names can only contain Letter Numbers Underline And must start with a letter or underscore

4. Volatile variables
  
5. Reference assignment of variable