PHP learning operator related concepts_PHP tutorial
/*Operation symbols (PHP) Operation symbols
*
* According to the functions of operation symbols, they are divided into:
* 1. Arithmetic operators + - * / % ++ --
* 2. String operator. Connection operator
* 3. Assignment operator = += -= *= /= %= .=
* 4. Comparison operator > = !==
* Comparison operator---Conditional operator---Relational operator
* Comparison There is only one result: boolean true false
* === When comparing, not only the content is required to be the same, but also the type is required to be the same
* !== When comparing, the content is not the same, but the type is also required to be different
* 5. Logical operators && or and || or or ! or not
* Logical operators can only operate on bool type values, and return bool type values
* 6. Bitwise operators & | ^ ~ > >>>
* 7. Other operators? : `` @ => -> :: & $
* `` Used to execute the operating system kernel
* @ is used to block error messages
* It is recommended to use "()" to change the priority of expressions
*
* % has two purposes: integer division operation; control range, do not use decimals, and Don't use negative numbers
* %. Convert the numbers on both sides of the operator to integers and then divide them to find the remainder.
*/
//Use the % symbol to determine leap years
$year=2011;
if(($year%4==0 && %year%100!=0) || $year% 400=0)
{
echo "run nian";
}
else
{
echo "not run nian";
}
// ++ --Use of symbols
$a=10;
$a++; //$a=$a+1; Use variables first, then increment by 1
++$a; //$a= $a+1; first increment by 1, then use variable
$a--; //$a=$a-1; first use variable, then decrement by 1
--$a; //$ a=$a-1; Decrement it by 1 first, then use the variable
echo $a; //The result is 10
//++ -- The difference in operations
$a=10;
$b=$a++;//b=10,a=11
$c=--$b;//c=9,b=9
$d=$c++ + ++$c; / /d=20,c=11
$e=$d-- - --$d; //d=18,e=2
echo $d;
//String operator. Use of
$name="tom";
$age=27;
$height=1.75;
echo "My name is: {$name} My age is: {$age }My height is: {$height} meters
";
echo 'My name is:'.$name.'My age is:'.$age.'My height is:' .$height.'米'.'
';
echo "$age=".$age; //$age=27
echo "My name is: {$name} mine Age is: {$age} My height is: {$height} meters
";//Use of assignment operator
$a=10;
$a+=10; //$a =$a+10;
$a-=10; //$a=$a-10;
$a*=10; //...
$a/=10; // ...
$a%=10; //$a=$a%10;
$a.="abc";//$a=$a."abc";
echo $ a;
$str='
'; $str.= ' | ';
echo $str;//Output a table
//Comparison operator
var_dump(15>6);//Return bool(true)
$a=15;
if(15==$a)
{
echo "a=15";
}
else
{
echo "a!=15";
}
//Use of logical operators
var_dump( true && true);//true
var_dump(true && false);//false
var_dump(true || false);//true
var_dump(!true);//false
var_dump(!false);//true
//Determine username and password
$username="admin";
$password="123456";
$email="290080604@qq.com ";
if($username=="admin" && $password="123456")
{
echo "The username and password are correct";
}
if($username== "" || $password=="" || $email=="")
{
echo "Not one can be empty";
}
//bit operator
$a=20; //00010100
$b=30; // 00011110
/*
* 20 00010100
* 30 00011110 &
*--------- --------------------------
* 00010100
*
*/
$c=$a & $ b;
echo $c;
/*In addition, & | can also be used for logical operations
* The short circuit problem of && and ||:
* && When doing operations, if the previous number is false, then whether the following number is true, the entire expression is false, so the following operands will not be executed;
* || During operation, if the previous number is true, then whether the following number is false, the entire expression is true, so the following operands will not be executed;
* However, when & or | are operated, both sides will be executed
*/
$a=10;
if($a>5 || $a++echo $a;//output 10
$b=10;
if($b>5 | $b++echo $b;//Output 11
/*
The concept of bit: a bit is composed of 8 binary numbers (for example, 00000000),
A byte consists of 8 bits, so there are 32 binary numbers.
Original code: The highest bit uses 0 to represent a positive number, 1 to represent a negative number
+7 00000111
-7 10000111
Complement code: If a number is positive, its complement code is the same as the original code ;
If a number is negative, the sign bit is 1, and the remaining bits are the inversion of the original code;
+7 00000111
-7 11111000
+0 00000000
-0 11111111
Complement code: If a number is positive, its complement and inverse code are the same as the original code
If a number is negative, its complement = complement code + 1, remove the highest overflow bit
-7 Original code 10000111 Inverse code 11111000
+1
Complement code 11111001
Given the complement code of a negative number, convert it into a decimal number.
1. Negate each digit first
2. Convert it to a decimal number
3. Add a negative sign and then subtract 1.
Example: complement 11111010
Negative 00000101
4+1=5
-5-1=-6
Bitwise operators:
& Bitwise AND | Bitwise OR ^Bitwise XOR~Bitwise negation
Example: Bitwise AND 01101101
&00110111
00100101
Conclusion: Only 1 1 is 1.
Bitwise OR 01101101
|00110111
01111111
Conclusion: Only 0 0 is 0.
Bitwise XOR 01101101
^00110111
01011010
Conclusion: Only 1 0 or 0 1 is 1. (It can also be understood as 1 (true) in different states)
Bitwise negation~00110111
11001000
Conclusion: Change 0 to 1 and 1 to 0
Shift operator:
Left shift:> Unsigned right shift:>>>
Example: Number x x>2 x>>> ;2
17 00010001 01000100 00000100 00000100
-17 11101111 10111100 11111011 00111011
Conclusion: Positive numbers are moved left and right to complement 0, negative numbers are shifted left to complement 0, and signed numbers are shifted to the right to complement 1. Sign complement 0
*/
//Application of other operators
$a=10;
$b=$a>5 ? $a : 5;//Ternary operator, if true $b =$a otherwise $b=5
echo $b;
//Use `` to execute operating system shell commands
$str=`ipconfig /all`;
echo '
'; <br>echo $str; <br>echo '';
?>

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values and handle functions that may return null values.

In PHP, use the clone keyword to create a copy of the object and customize the cloning behavior through the \_\_clone magic method. 1. Use the clone keyword to make a shallow copy, cloning the object's properties but not the object's properties. 2. The \_\_clone method can deeply copy nested objects to avoid shallow copying problems. 3. Pay attention to avoid circular references and performance problems in cloning, and optimize cloning operations to improve efficiency.

PHP is suitable for web development and content management systems, and Python is suitable for data science, machine learning and automation scripts. 1.PHP performs well in building fast and scalable websites and applications and is commonly used in CMS such as WordPress. 2. Python has performed outstandingly in the fields of data science and machine learning, with rich libraries such as NumPy and TensorFlow.

Key players in HTTP cache headers include Cache-Control, ETag, and Last-Modified. 1.Cache-Control is used to control caching policies. Example: Cache-Control:max-age=3600,public. 2. ETag verifies resource changes through unique identifiers, example: ETag: "686897696a7c876b7e". 3.Last-Modified indicates the resource's last modification time, example: Last-Modified:Wed,21Oct201507:28:00GMT.

In PHP, password_hash and password_verify functions should be used to implement secure password hashing, and MD5 or SHA1 should not be used. 1) password_hash generates a hash containing salt values to enhance security. 2) Password_verify verify password and ensure security by comparing hash values. 3) MD5 and SHA1 are vulnerable and lack salt values, and are not suitable for modern password security.

PHP is a server-side scripting language used for dynamic web development and server-side applications. 1.PHP is an interpreted language that does not require compilation and is suitable for rapid development. 2. PHP code is embedded in HTML, making it easy to develop web pages. 3. PHP processes server-side logic, generates HTML output, and supports user interaction and data processing. 4. PHP can interact with the database, process form submission, and execute server-side tasks.

PHP has shaped the network over the past few decades and will continue to play an important role in web development. 1) PHP originated in 1994 and has become the first choice for developers due to its ease of use and seamless integration with MySQL. 2) Its core functions include generating dynamic content and integrating with the database, allowing the website to be updated in real time and displayed in personalized manner. 3) The wide application and ecosystem of PHP have driven its long-term impact, but it also faces version updates and security challenges. 4) Performance improvements in recent years, such as the release of PHP7, enable it to compete with modern languages. 5) In the future, PHP needs to deal with new challenges such as containerization and microservices, but its flexibility and active community make it adaptable.

The core benefits of PHP include ease of learning, strong web development support, rich libraries and frameworks, high performance and scalability, cross-platform compatibility, and cost-effectiveness. 1) Easy to learn and use, suitable for beginners; 2) Good integration with web servers and supports multiple databases; 3) Have powerful frameworks such as Laravel; 4) High performance can be achieved through optimization; 5) Support multiple operating systems; 6) Open source to reduce development costs.


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