PHP basic syntax quick start manual-PHP Problem-php.cn

PHP basic syntax quick start manual

This article shares with you some knowledge about basic PHP syntax. It is of great reference value for some beginners. I hope it can help everyone.

The suffix of the php script is named .php, and the code is placed in the following brackets:

 <?php ....... ?>

Copy after login

echo can print information, similar to printf.

 <?php 
 echo "hallo world"; 
 ?>

Copy after login

End each statement with a semicolon;.

php supports three comment methods:

 <?php 
 // 第一种 
 # 第二种 
 /* 这是 多行 注释 */ 
 ?>

Copy after login

In php, the capitalization of functions, classes, and keywords are the same:

 <!DOCTYPE html> 
 <html> 
 <body> 
 <?php 
     ECHO "Hello World!<br>"; 
     echo "Hello World!<br>"; 
     EcHo "Hello World!<br>"; 
 ?>
 </body> 
 </html>

Copy after login

However, all variables are case-sensitive and need to be case-sensitive.

 <?php 
     $color="red"; 
     $Color="black"; 
     echo "my car is " . $color . "<br>"; 
     echo "my car is " . $Color . "<br>"; 
 ?>

Copy after login

The above example also points out the syntax of variable definition and string concatenation.

Variable naming rules:

PHP variable rules:

Variables start with the $ symbol, followed by the name of the variable
The variable name must Start with a letter or underscore
Variable names cannot start with numbers
Variable names can only contain alphanumeric characters and underscores (A-z, 0-9, and _)
Variable names Case sensitive ($y and $Y are two different variables)
Variables will be created the first time they are assigned. There is no need to declare the type of the variable.

Variables will have three different scopes:

PHP has three different scopes of variables:

local (local)
global (global)
static (static)

Variables declared outside the function have Global scope and can only be accessed outside the function.
Variables declared inside a function have LOCAL scope and can only be accessed inside the function.
The following example tests variables with local and global scopes:

 <?php 
 $x=5; // 全局作用域 
 function myTest() { 
 $y=10; // 局部作用域 
 echo "<p>测试函数内部的变量：</p>"; 
 echo "变量 x 是：$x"; 
 echo "<br>"; 
 echo "变量 y 是：$y"; 
 } 
 myTest(); 
 echo "<p>测试函数之外的变量：</p>"; 
 echo "变量 x 是：$x"; 
 echo "<br>"; 
 echo "变量 y 是：$y"; 
 ?>

Copy after login

Running results:

Variables inside the test function:

Variable x is:
Variable y is: 10
Variables outside the test function:

Variable x is: 5
Variable y is:
What is strange is why global variables cannot be Access within local functions.

In fact, it can be accessed, but it requires the help of the global keyword:

The global keyword is used to access global variables within the function.
To do this, use the global keyword in front of the variable (inside the function):

<?php
$x=5;
$y=10;

function myTest() {
 global $x,$y;
 $y=$x+$y;
}

myTest();
echo $y; // 输出 15
?>

Copy after login

PHP also stores all in an array called $GLOBALS[index] global variables. The subscript holds the variable name. This array is also accessible within the function and can be used to directly update global variables.

<?php
$x=5;
$y=10;

function myTest() {
 $GLOBALS[&#39;y&#39;]=$GLOBALS[&#39;x&#39;]+$GLOBALS[&#39;y&#39;];
} 

myTest();
echo $y; // 输出 15
?>

Copy after login

Normally, all variables are deleted when the function completes execution. However, sometimes I need to not delete a local variable. To achieve this, static:

(recommended learning: php course)

<?php

function myTest() {
 static $x=0;
 echo $x;
 $x++;
}

myTest();
myTest();
myTest();

?>

Copy after login

Both echo and print can be used in php, the only difference between them is The difference is that print returns 1 and echo has no return value.

The strlen function can return the length of the string.

The strpos function is used to determine the position of another string:

 <?php 
 echo strpos("Hello world!","world"); 
 ?>

Copy after login

Use the define function to define constants:

 <?php 
 define("GREETING", "Welcome to W3School.com.cn!"); 
 echo GREETING; 
 ?>

Copy after login

There is a third define function Parameter used to specify whether it is case sensitive.

PHP’s if-else statement is similar to other languages. For example:

<?php
$t=date("H");

if ($t<"10") {
 echo "Have a good morning!";
} elseif ($t<"20") {
 echo "Have a good day!";
} else {
 echo "Have a good night!";
}
?>

Copy after login

switch-case statement:

<?php
switch ($x)
{
case 1:
 echo "Number 1";
 break;
case 2:
 echo "Number 2";
 break;
case 3:
 echo "Number 3";
 break;
default:
 echo "No number between 1 and 3";
}
?>

Copy after login

while, for statement and others There is no difference in language, take a look at foreach:

<?php 
$colors = array("red","green","blue","yellow"); 

foreach ($colors as $value) {
 echo "$value <br>";
}
?>

Copy after login

The real power of php comes from its functions, it has 1000 built-in functions.

User-defined function declarations start with the word "function":

function functionName() {
   被执行的代码;
 }

Copy after login

For example:

<?php
function writeMsg() {
 echo "Hello world!";
}

writeMsg(); // 调用函数
?>

// 含参数
<?php
function familyName($fname,$year) {
 echo "$fname Zhang. Born in $year <br>";
}

familyName("Li","1975");
familyName("Hong","1978");
familyName("Tao","1983");
?>

// 默认参数
<?php
function setHeight($minheight=50) {
 echo "The height is : $minheight <br>";
}

setHeight(350);
setHeight(); // 将使用默认值 50
setHeight(135);
setHeight(80);
?>

// 返回值
<?php
function sum($x,$y) {
 $z=$x+$y;
 return $z;
}

echo "5 + 10 = " . sum(5,10) . "<br>";
echo "7 + 13 = " . sum(7,13) . "<br>";
echo "2 + 4 = " . sum(2,4);
?>

Copy after login

In PHP, there are three Array types:

Indexed array - array with numeric index
Associative array - array with specified key
Multidimensional array - contains one or more Array of arrays

Index array:

$cars=array("Volvo","BMW","SAAB");
<?php
$cars=array("Volvo","BMW","SAAB");
echo "I like " . $cars[0] . ", " . $cars[1] . " and " . $cars[2] . ".";
?>

// count
<?php
$cars=array("Volvo","BMW","SAAB");
echo count($cars);
?>

// 变量索引数组
<?php
$cars=array("Volvo","BMW","SAAB");
$arrlength=count($cars);

for($x=0;$x<$arrlength;$x++) {
 echo $cars[$x];
 echo "<br>";
}
?>

Copy after login

Associative array:

 $age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");

Copy after login

$age[&#39;Peter&#39;]="35";
$age[&#39;Ben&#39;]="37";
$age[&#39;Joe&#39;]="43";

<?php
$age=array("Bill"=>"35","Steve"=>"37","Peter"=>"43");
echo "Peter is " . $age[&#39;Peter&#39;] . " years old.";
?>




// 遍历
<?php
$age=array("Bill"=>"35","Steve"=>"37","Peter"=>"43");

foreach($age as $x=>$x_value) {
 echo "Key=" . $x . ", Value=" . $x_value;
 echo "<br>";
}
?>

Copy after login

Array sorting methods are The following:

sort() - Sorts an array in ascending order
rsort() - Sorts an array in descending order
asort() - Sorts an array based on value, in order Sort associative array in ascending order
ksort() - Sort associative array in ascending order based on key
arsort() - Sort associative array in descending order based on value
krsort() - Sorts an associative array in descending order by key

What is more difficult to understand is key-value sorting.

<?php
$age=array("Bill"=>"35","Steve"=>"37","Peter"=>"43");
asort($age);
?>

<?php
$age=array("Bill"=>"35","Steve"=>"37","Peter"=>"43");
ksort($age);
?>

Copy after login

Super global variables, which are predefined global variables, can be used everywhere and have special meanings:

$GLOBALS: refers to those available in the global scope All variables
$_SERVER: holds information about headers, paths and script locations.
$_REQUEST: used to collect data submitted by HTML forms.
$_POST: used to collect form data after submitting the HTML form with method="post". Also commonly used to pass variables.
$_GET:$_GET can also be used to collect form data after submitting an HTML form (method="get").
$_FILES
$_ENV
$_COOKIE
$_SESSION

Other content can be found in form processing.

If you want to learn more about php, please visit the php Chinese website.