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

<?php
?>

• 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

    $a=1;
    $str="Hello";
    #This output variable must be followed by a space, otherwise an error will be reported
    echo "$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

**Example:**

    $a=100;
    function demoTest(){
        $b=50;
        echo "<p>Function internal test</p>";
        echo "variable a=".$a."<br>";
        echo "variable b=".$b;
    }
    demoTest();
    echo "<p>Function external test</p>";
    echo "variable a=".$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

    $x=100;
    $y=50;
    $t=0;
    function Test(){
        global $x,$y;
        $y+=$x;
        $GLOBALS['t']=$GLOBALS['x']+$GLOBALS['y'];
    }
    Test();
    echo $y;  //150
    echo "<br>".$t;  //=100+150

static

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>";
        $x++;
    }
    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)

    $x=10;
    $y=0xABCDE;
    $m=07777;
    //var_dump returns the data type and value
    var_dump($x); //int(10)
    $n=10.5;
    var_dump($n); // float(10.5)
    $flag=true;
    var_dump($flag); //bool(true)

other

1. array

2. object

3. null

Set the value to null and empty the variable

php operator

Arithmetic operator

+，-，*，/，%

Assignment Operators

=，+=，-=，*=，/=，%=

String operator

    $str1="Hello";
    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

==，!=，>，<，<=，>=

Extension:

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

    $x=5;
    $y=5;
    $z="5";
    var_dump($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;
    }
    Test();
    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