PHP learning operator related concepts

The code is as follows:
/*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
* There is only one result after comparison: boolean true false
* === When comparing, not only the content must be the same , also requires the same type
* !== When comparing, the content is different, and the type is also required
* 5. Logical operators && or and || or or ! or not
* Logical operators can only operate on bool type values , the value returned is also a bool type
* 6. Bitwise operator & | ^ ~ > >>>
* 7. Other operators? : `` @ => -> ; :: & $
* `` Used to execute the operating system kernel
* @ Used to shield error messages
* It is recommended to use "()" to change the priority of expressions
*
* % has two purposes: integer division operation ; To control the range, do not use decimals or negative numbers
* %. Convert the numbers on both sides of the operator to integers and then divide them to find the remainder.
*/
//Use % symbol to determine leap year
$year=2011;
if(($year%4==0 && %year%100!=0) || $year%400=0)
{
echo "run nian";
}
else
{
echo " not run nian";
}
// ++ --Use of symbols
$a=10;
$a++; //$a=$a+1 ; First use the variable, then increment it by 1
++$a; //$a=$a+1; First use it and then increment it by 1, then use the variable
$a--; //$a=$a-1; First Use a variable, then decrement it by 1
--$a; //$a=$a-1; Decrement it by 1 first, then use the variable
echo $a; //The result is 10
//++ -- Operational Difference
$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;
//Usage of string operator.
$name="tom";
$age=27;
$height=1.75;
echo "My name is: {$name} My age is: {$age} My height is: {$height} m
";
echo 'My name is: '.$name.' My age is: '.$age.' My height is: '.$height.'m'.'
echo "$age=".$age; //$age=27
echo "My name is: {$name} My age is: {$age} My height is: {$height} m
";//Usage 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.='';
$str.='< ;td>';
$str.='';
$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 the 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 "No 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
* && and || Short-circuit problem:
* && 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;
* || When doing operations , 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: one bit is composed of 8 binary Composed of 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
Inverse code: If a number is positive, its inverse code is the same as the original code;
If a number is negative, Then the sign bit is 1, and the remaining bits are the inversion of the original code;
+7 00000111
-7 11111000
+0 00000000
-0 11111111
Complementary code: If a number is positive, its complement and complement are the same as The original code is the same
If a number is negative, its complement = one's complement + 1, remove the highest overflow bit
-7 Original code 10000111 , convert it to 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: Two’s complement code 11111010
Negation 00000101
4+1=5
-5-1=-6
Bit 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: 1 when only 1 0 or 0 1. (It can also be understood as 1 (true) in different states)
Bitwise negation~00110111
11001000
Conclusion: Change 0 to 1, 1 to 0
Shift operator:
Left shift: > Unsigned right shift: >>>
Example: Number x 11101111 10111100 11111011 00111011
Conclusion: Positive numbers are moved left and right to complement 0, negative numbers are shifted left to complement 0, signed right shifts are complemented by 1, and unsigned shifts are complemented by 0
*/
//Use 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 command
$str=`ipconfig /all`;
echo '

'; <br>echo $str; <br>echo '

';
?>