Operators in PHP and PHP knowledge base

Preface

In the previous chapter, we had a preliminary understanding of the web page basics of PHP and the entry-level basics of PHP. Today we will continue to share more information with you. Knowledge of PHP.

Theoretical knowledge may seem boring, but our practice (coding) is inseparable from it after all.

Only by combining theory with practice, more functions can be achieved with the least amount of code.

***Keywords in this chapter: Operator; variable variable; addressing symbol; branch and Loop; Flow control statement goto.

Now, let’s take a look at # in PHP ##Operators and more PHP knowledge base：

一Operator

1. Arithmetic operators: + - * / % ++ --

2. Assignment operator: = += -= *= /= %= .= (connection string)

3. Comparison operators: > < >= <= == === <>,! =! ==

==: Requires equal values, but does not require equal data types

===: Requires Values ​​and data types must be equal

!=: Only values ​​are compared, and equal values ​​are false

!= =: Compare values ​​and types. If both values ​​and types are equal, false

4. Logical operators: and/&& or/|| not/ ! When xor

##&& and || are operated, a short circuit will occur:

When the result can be judged on the left side, it will no longer be executed. Right! ! (When the left side of && is false, the result is false; when the left side of || is true, the result is true)

xor: Logical XOR. If only one of the two sides is correct, the result is true; if both sides are true or both are false, the result is false.

5. Bit operators:

Convert decimal to binary and then perform operations.

&: Bitwise AND, after converting to binary, both are 1, and the result is 1
|: Bitwise OR, after converting to binary, one is 1 1, is 1
^: Bitwise XOR, after converting to binary, if the two are not the same, they are 1; if both are 1, or both are 0, the result will be 0.
~: Bitwise inversion, after converting to binary number, all digits are inverted. 1--->0 0--->1
<<: Left shift: After converting to binary, shift the number of bits to the left and fill the remaining digits on the right with 0.
num << n is equivalent to num*2^n (※※※)
>>: Right shift: After converting to binary, right Shift a few bits and fill the remaining digits on the left with 0s.
num >> n is equivalent to num/2^n (※※※)

6. Other operators:
Expression 1?Expression 2:Expression 3:
If expression 1 is true, execute expression 2, otherwise execute expression 3
`` : Call the command line in the system DOS environment and execute it. However, due to security and cross-platform nature, we do not support the use; eg:`ipconfig`
@: Error message control character: some small error messages can be temporarily blocked. But its use is not recommended!

二Variable variable

In front of a variable name, add a $ symbol. You can use the value of the first variable as the name of the new variable.

$hello = "hello1";
$$hello = "world";//$hello1
$$$hello = "Jredu";//$world

##三Address symbol

&: Adding & before the variable name can take out the address of the variable in memory and assign it to another variable.
$num2 = &$num1;//Take out the address of num1 and give it to num2, which is equivalent to the reference data type we are talking about. The values ​​of num2 and num1 will change simultaneously.

四Branch and loop

1. Judgment conditions in if
For details, please click "Click me if you are curious!"The second part of the previous chapter [Basics of PHP entry], Here, the blogger will not introduce them one by one...

2. elseif
#In PHP, elseif statements can be written consecutively , or can be separated by spaces;

For example:
else if() √
elseif() √

3. switch
In PHP, when judging the switch structure, use == instead of ===
In PHP, continue can be used in the switch structure and has the same effect as break.
In php, continue and break can be followed by numbers, indicating how many levels of loops to skip or switch;
eg:break 3; means terminating the 3-level loop

4. Do-while loop
A semicolon must be added at the end of the do-while loop.
do{

}while();

5. Process control Statement

1. break: Terminate the loop of this level; break can be followed by a number to indicate how many levels of loops to terminate. break 3, terminate the 3-level loop.
2. continue: skip this loop; continue can also be followed by a number to indicate how many levels of loops to skip
3. return: terminate the current function and Return value (if any), but it is generally only used in functions. It is not recommended to use return in scripts;
4. exit(mixed conclusion)/die(mixed conclusion) function: end directly Current PHP script! !
If there are parameters passed in, the closing statement will be printed first, and then the current script will end.

##五Flow control statement goto

##1. Usage:

Define a jump anchor point, "identifier"-->"jr:"

Set a goto statement at any position and jump to the specified anchor point: "goto jr;"

2. Function:
When encountering a goto statement, jump directly to the set identifier position.

3. Used to implement branches.
Note: The goto statement only allows the current program control flow to jump to the specified anchor point, but is not responsible for executing several lines of code.
That is, all codes from the anchor point downwards will be executed in sequence. If multiple branches are implemented, goto statements must be used to skip other branches. (See the case below for details)

4. Goto implementation loop:

See the case for details. However, in goto, break cannot be used to break out of a loop.

5. Advantages and disadvantages of goto statement:
① Advantages: Flexible and convenient to use, instruction-level statements, faster efficiency, better performance .
② Disadvantages: The extensive use of goto is a disaster for the structuring of the code.
It is not conducive to a clear code structure and understanding of the code, and it is very likely to skip some important declaration statements, resulting in code errors.

Theory is not as good as practice. For details, see the code below↓↓↓

 1 //goto语句实现分支 2    /*$num = true; 3    if(!$num){ 4        goto jh; 5    }else{ 6        goto jr; 7    } 8     9    jr:10    echo "3333333333333<br />";11    echo "4444444444444<br />";12    goto jj;13    14    jh:15    echo "5555555555555<br />";16    echo "6666666666666<br />";17    18    jj:*/19    20    //[1]goto循环21    $num = 0;22    jr:23    echo "1222222222221<br />";24    $num ++;25    if($num<5){26        goto jj;//通过goto跳出循环，注意不能使用break27    }28    goto jr;29    30    jj:31    echo "hahaha";32    33    /*//[2]goto实现循环34     $num=0;35     jr:36     echo"11111<br>";37     $num++;38     if($num<5){39         goto jr;40     }*/

The above is what I want to share with you today. I hope it will be helpful to you~

The blogger reminds everyone again that theoretical knowledge is the basis for good code and cannot be ignored. ! [Basic Introduction to PHP] will continue to be updated, thank you for your attention~~~

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