php basic syntax

php basic syntax

The php script executes on the server and sends the pure HTML results back to the browser

Basic grammar

  • Beginning and end
  • The file extension is. php
  • Each line of code must end with a semicolon

php output

  • echo and print, which can contain HTML tags

echo: you can output one or more strings

print: only one string is allowed to be output, and the return value is always 1

    #This output variable must be followed by a space, otherwise an error will be reported
    echo "$str World!$a <br>";
    #==There is no need to add a space for this
    echo "{$str} World!{$a} <br>";
    #Multiple strings, using,
    $str2="I love php!";
    echo "This"," is"," my first"," php process.",$str2,"<br>";
    #Connect multiple strings, using
    echo $str.$str2." ".$a;

php comments

  • Single line / / or#
  • Multiline / **/
  • Document comments / * **/
	#No output
    //No output
        No output
     * No output

php variable

  1. Define variable: $variable name = variable value
$a = 1;
echo $a;
$b = 2;
$c = 3;
echo $b;
echo $c;

matters needing attention:

  • To be expressed in $
  • Start with a letter or underscore
  • Variable names can only consist of letters, numbers, and underscores
  • Cannot contain spaces, separated by underscores
  • Variable names are case sensitive
  • Keywords cannot be used as variable names

php variable scope

php has three different variable scopes

  1. Local (local)
  2. Global
  3. Static

local and global

  • Variables declared outside the function have global scope and can only be accessed outside the function
  • Variables declared within a function have local scope and can only be accessed inside the function


    function demoTest(){
        echo "<p>Function internal test</p>";
        echo "variable a=".$a."<br>";
        echo "variable b=".$b;
    echo "<p>Function external test</p>";
    echo "variable a=".$a,"<br>";
    echo "variable b=".$b;
*Function internal test
*Variable a=
*Variable b=50
*Function external test
*Variable a=100
*Variable b=
#External can only access external, internal can only access internal

Use the global keyword to access global variables, or use $GLOBALS ['variable name']. This array stores all global variables and can be accessed inside and outside

    function Test(){
        global $x,$y;
    echo $y;  //150
    echo "<br>".$t;  //=100+150


The static modified variable will be retained after the calling function is executed, but it is still a local variable

    function Test(){
        static $x=0;
        echo $x."<br>";
    Test(); //0
    Test(); //1
    Test(); //2
    Test(); //3

php data type

php is a weakly typed language and does not need to specify data types

Four scalar types

  1. character string
  2. Integers (three: decimal, hexadecimal and octal) are similar to Java and lower case
  3. Floating point number
  4. Boolean (only true and false)
    //var_dump returns the data type and value
    var_dump($x); //int(10)
    var_dump($n); // float(10.5)
    var_dump($flag); //bool(true)


  1. array

  2. object

  3. null

Set the value to null and empty the variable

php operator

Arithmetic operator


Assignment Operators


String operator

    echo $str1." World!"; //Hello World!
    echo "<br>";
    $str1.=" World!";
    echo $str1;           //Hello World!
  • . concatenation is equivalent to Java string addition+
  • . = serial assignment is equivalent to+=

Increment / decrement operator

  • $x++ , ++$x
  • $x-- , --$x

Comparison operator



  1. =Congruent (identical), $x$y and equal types return true
  2. < > not equal to
  3. !=== Incomplete (completely unequal). If $x is not equal to $y, or the type is different, return true
    var_dump($x===$y);  //true
    echo "<br>";
    var_dump ($x!==$z);  //true

Logical operator

&& and , || or , !

XOR (exclusive or) $x and $y have only one true value, and return true

Array Operations

Used to compare arrays

+Union, = = equal, = congruent (same order)= Not equal to, < > not equal to! Incomplete (completely different)

php constant

Cannot change the value of. Constants are automatically global

Use the define() function

Three parameters:

  1. The name of the constant
  2. Constant value
  3. Specifies whether the constant name is case sensitive. The default value is false
    define("GOOGLE","I'm google.");
    echo GOOGLE;
    echo "<br>";
    define("MICRO","I'm Microsoft");
    function Test(){
        echo MICRO;
    echo "<br>";
    echo MICRO;

php string function

Common string operation functions

  • php strlen() function

Length of returned string = Java: str.length();

  • php str_word_count()

Counts the words in the string

  • php strrev()

Reverse string

  • php strpos()

Retrieves the specified character or text within a string

If found, the first matching character position will be returned; if not found, false will be returned

  • php str_replace()

Replace some characters in the string with some strings

Three parameters: 1. Find value 2. Replace value 3. Search string

    $str="this is php";
    echo strlen($str)."<br>";  //11
    echo str_word_count($str),"<br>";  //3
    echo strrev($str)."<br>";
    echo strpos($str,"is"); //2. Index 2 appears is for the first time
    echo "<br>";
    echo str_replace("php","Java",$str); //this is Java

Posted by H-Fish on Wed, 10 Nov 2021 22:00:56 -0800