Chapter 2 PHP basic php code writing

2020-05-10 17:51:37
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1. Several styles of embedding PHP code on the web page
Standard style or short style is recommended

 
<?php 
// The standard style  
echo 'Hello World!'; 
?> 
<? 
// Brief style  
echo 'Hello World!'; 
?> 
<script language="php"> 
//script style  
echo 'Hello World!'; 
</script>

2. Four ways to comment code

 
<?php 
// Single-line comments  
/* 
*  Multiline comment  
*/ 
#shell Style comments  
/** 
* PHPdoc Style comments  
*/ 
?>

3. Several ways to output a string to a browser

 
<?php 
/* 
* echo The output () function outputs a string to the browser  
*  Function return value: void 
*/ 
echo 'echo function!'; 
echo('<br/>'); 
/* 
* echo The output () function outputs a string to the browser  
*  Function return value: int 
*/ 
print 'print function'; 
echo('<br/>'); 
echo print 'echo value of print function. '; 
echo('<br/>'); 
/* 
* printf The output () function outputs a string to the browser  
*  Function returns the length of the printed string  
*/ 
printf("a weekend have %d days",7); 
echo('<br/>'); 
echo printf("a weekend have %d days",7); 
echo('<br/>'); 
/* 
* sprintf The string () function saves a string to memory  
*  Function returns value: the saved string itself  
*/ 
sprintf('sprintf function'); 
echo('<br/>'); 
echo sprintf('sprintf function'); 
echo('<br/>'); 
?>

Output results:
echo function test!
print function test.
print function test. 1
a weekend have 7 days
a weekend have 7 days. 23
sprintf function test
Common type indicators

type

describe

Integer, shown in base 2

Integer, shown as the ASCII character

An integer, shown as a signed decimal number

A floating point number that is displayed as a floating point number

An integer, shown as a base 8 number

String, which is displayed as a string

An integer, shown as an unsigned decimal number

An integer, shown as a lowercase base 106 number

An integer, shown as an uppercase base 106 number

4. Identifiers and variables
1. Basic rules for identifiers:
1) the identifier can be of any length and can be composed of any letter, number and underscore.
2) the identifier cannot start with a number.
3) in PHP, identifiers are case sensitive.
4) a variable name can be the same as a function name.
2. Variable assignment:

 
<?php 
$sum = 0; 
$total = 1.22; 
$sum = $total; 
echo $sum;　//1.22 
?>

3. Data type of variables:
Basic data type

type

The name of the

Integer

The integer

Float

Single precision floating point number

Double

And precision floating point Numbers

String

string

Boolean

Array

An array of

Object

object

4. Type strength
PHP is a dynamic language, which is a very weak type language. It can dynamically change the type of variables while the program is running.
5. Type conversion:
Implicit type conversion:

 
<?php 
$sum = 0; 
$total = 1.22; 
$sum = $total; 
echo gettype ( $sum );//double 
?>

Explicit type conversion:

 
<?php 
$sum = 100; 
$total = ( string ) $sum; 
echo gettype ( $sum );//string 
?>

Type conversion is performed using the settype() function, with the return value of 1 indicating success and null indicating failure.

 
<?php 
$sum = 58; 
echo settype ( $sum, "float" ); 
echo $sum; //58 
echo gettype ( $sum ); //double 
?>

6. Function of testing variables:

function

The return value

Gettype()

Gets the type of the variable

One of the basic data types

Settype()

sets the type of the variable

Bool(1:true 0:false(or ''))

Isset()

To determine whether a variable exists

Bool

Unset()

Release the given variable

Void

Empty()

Detects whether the value of 1 variable is empty

Bool

is_int() is_integer()

Detects whether the variable is an integer

Bool

Is_string()

Detects whether the variable is a string

bool

Is_numeric

Detects whether a variable is a number or a numeric string

bool

Is_null

Test whether the variable is NULL

bool

Intval()

Gets the integer value of a variable

int

Basic use of Isset()

 
<?php 
$a = 10; 
echo isset ( $a );//1 
?> 
<?php 
echo isset ( $b );//'' 
?>

Basic use of Usset()

 
<?php 
$a = 10; 
unset($a); 
echo isset ( $a );//'' 
?>

Basic use of Empty()

 
<?php 
$a= 5; 
$b =1; 
$c = 0; 
$d = ""; 
$e = array(); 
$f = null; 
$g = "0"; 
$h = false; 
echo empty($a);//''(false) 
echo '<br/>'; 
echo empty($b);//''(false) 
echo '<br/>'; 
echo empty($c);//1(true) 
echo '<br/>'; 
echo empty($d);//1(true) 
echo '<br/>'; 
echo empty($e);//1(true) 
echo '<br/>'; 
echo empty($f);//1(true) 
echo '<br/>'; 
echo empty($g);//1(true) 
echo '<br/>'; 
echo empty($h);//1(true) 
echo '<br/>'; 
echo empty($f);//1(true) 
?>

Basic use of is_int(). Similar functions are :is_float(), is_double(), is_string(), is_bool(), is_array(), is_object(), is_resource(), is_numeric(), is_is_es264 EN (), etc.

 
<?php 
$a = 11; 
$b = 1.23; 
$c = 3.1415926; 
$d = "hello"; 
$e = false; 
$f = array(); 
$g = null; 
echo is_int($a);//1 
echo '<br/>'; 
echo is_float($b);//1 
echo '<br/>'; 
echo is_double($c);//1 
echo '<br/>'; 
echo is_string($d);//1 
echo '<br/>'; 
echo is_bool($e);//1 
echo '<br/>'; 
echo is_array($f);//1 
echo '<br/>'; 
echo is_null($g);//1 
echo '<br/>'; 
echo is_numeric($a);//1 
?>

Basic use of the Intval() function. Similar functions are: floatval(), strval()

 
<?php 
$a = 22.23; 
echo gettype($a);//double 
echo '<br/>'; 
$b = intval($a);// The type does not change after conversion $a Original type  
echo gettype($a);//double 
echo '<br/>'; 
?> 
<?php 
$a = 22.23; 
echo gettype($a);//double 
echo '<br/>'; 
settype($a,"integer");// It changes after the type conversion $aa Original type  
echo gettype($a);//integer 
echo '<br/>'; 
?>

7. Scope of variables

Super global variable

The variable name

role

$GLOBALS

Array of all global variables

$_SERVER

Array of server environment variables

$_GET

The array of variables passed to the script via GET

$_POST

The array of variables passed to the script via POST

$_COOKIE

COOKIE variable array

$_FILES

Array of variables associated with file upload

$_ENV

Array of environment variables

$_REQUEST

The array of variables used for user input

$_SESSION

Array of session variables

8. Constant
Once 1 is defined, it cannot be changed again.

 
<?php 
define("TOTAL",100); 
echo TOTAL;//100 
echo '<br/>'; 
define("TOTAL",200); 
echo TOTAL;//100 
?>

Method to view PHP predefined constants

 
<?php 
phpinfo(); 
?>

Methods that reference PHP predefined constants

 
<?php 
echo $_SERVER["SERVER_NAME"];//localhost 
echo '<br/>'; 
echo $_SERVER["SERVER_PORT"];//8090 
echo '<br/>'; 
echo $_SERVER["DOCUMENT_ROOT"];//D:/AppServ/www 
echo '<br/>'; 
?>

5. Access form variables
Three common ways

 
<?php 
echo $username;// Short style, easy to confuse with variable names, not recommended.  
echo '<br/>'; 
echo $_POST['username'];// Medium style, 4.1.0 Version after support, recommended  
echo '<br/>'; 
echo $HTTP_POST_VARS['username'];// Verbose style, out of date, may be eliminated in the future  
?>

Posttest.html

 
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 
<html> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 
<title> How to get form data </title> 
</head> 
<body> 
<form method="POST" action="demo10.php"> 
username:<input type="text" name="username" /> 
<input type="submit" value="submit" /> 
</form> 
</body> 
</html>

6. String concatenation.

 
<?php 
echo "the student name is  : ".$_POST['username']; 
echo "<br/>"; 
echo "welcome to "."school"; 
?>