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 ....... ?>
echo can print information, similar to printf.
<?php echo "hallo world"; ?>
End each statement with a semicolon;.
php supports three comment methods:
<?php // 第一种 # 第二种 /* 这是 多行 注释 */ ?>
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>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>";
?>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";
?>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
?>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() {
$GLOBALS['y']=$GLOBALS['x']+$GLOBALS['y'];
}
myTest();
echo $y; // 输出 15
?>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();
?>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");
?>Use the define function to define constants:
<?php
define("GREETING", "Welcome to W3School.com.cn!");
echo GREETING;
?>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 ($t<"20") {
echo "Have a good day!";
} else {
echo "Have a good night!";
}
?>switch-case statement:
<?php
switch ($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";
}
?>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>";
}
?>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;
}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);
?>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>";
}
?>Associative array:
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");or
$age['Peter']="35";
$age['Ben']="37";
$age['Joe']="43";
<?php
$age=array("Bill"=>"35","Steve"=>"37","Peter"=>"43");
echo "Peter is " . $age['Peter'] . " 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>";
}
?>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);
?>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.
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