Summary of common special operators and functions in PHP (required for beginners of php)

New users often have some PHP special symbols. here we will sort out the commonly used special symbols. If you use all of them, it's time to learn more. Annotation symbol:
// Single line annotation
Multiline annotation
Use of quotation marks
''Single quotes, a simple string that can be taken without any processing;
"" Double quotes, php dynamic processing and output, usually used to process $ variables.
Boolean variable:
True is true;
The other is false.
Common variables:
String (numbers, Chinese characters, etc)
Integer (1, 2, 3, 4, 5, 0,-1,-2, and so on)
Double floating point number (decimal point)
Array
Object
Available methods include gettype ($ mix) and settype ($ mix, $ typename );

Common escape characters:

\ "Double quotation marks
\ Backslash
\ N line feed
\ R return to the beginning of the line
\ T horizontal tabulation
Operator Number:
+ Addition operation-subtraction operation
* Multiplication/Division
% Return remainder + + auto-Increment 1
-- Auto-subtract 1. connect two strings
Assignment operation:
= Place the value on the right to the left
+ = Add the right value to the left
-= Reduce the value on the right to the left
* = Multiply the value on the left by the value on the right.
/= Divide the value on the left by the value on the right
. = Add the string on the right to the left
Bitwise operation:
& Bitwise AND
| By bit or
^ Xor)
<Shifts 1 to the left
> Shifts one digit to the right.
~ Population
Logical operation:
<Less> greater
<= Less than or equal to> = greater than or equal
! = Not equal &
| Or! Non
Other operators
$ Variable symbol
& Alias for variables
@ Do not display the error message (before the function)
-> Object methods or attributes
=> Array element value
? : Ternary operator

Common Basic methods:

1. PHP converts strings to uppercase and lowercase!

Strtolower (); converts characters to lowercase letters
Strtoupper (); converts uppercase letters

2. PHP encrypted string

Unrecoverable:
Md5 ();
Sha1 ();
Recoverable:
Base64_encode ();
Base64_decode ();

3. quotation marks

I. single quotes are output as is
2. double quotation marks are output based on content interpretation
3. a single quotation mark (small quotation mark) is used to execute a system command, such as 'dir '. Table names and field names are commonly used.
4. "\" acts on translated characters. for example, "\ n" is a line break.

4. Functions: htmlspecialchars () and htmlentities ()
This function converts special characters into HTML strings (&....;). The most common use case may be the message board for handling customer messages.

& (And) &
"(Double quotation marks)"
<(Less than) to <
> (Greater than) to>
(Space) to convert

5. batch output HTML content!

Echo <EOT
HTML output content... // Comments are output here!
EOT;

Print < HTML output content... // Comments are output here!
EOT;
(Note: "{variable}" is used for internal variables }")

6. determine whether the file exists and the output content is file_exists ()

$ FileName = "File. TXT ";
If (file_exists ($ FileName )){
Echo"

".file_get_contents($FileName)."

";
} Else
{
Echo "no ";
}
?>

7. delete the variable to release the memory unset ();

Unset ($ var );
Unset ($ var, $ var1 );

8. is_numeric;
Checks whether the variable is a number;

9. is_int;
Checks whether the variable is an integer;

10. is_null;
Checks whether the variable is NULL;

11. is_string
Checks whether the variable is a string.

12. is_real;
Is_float () alias

13. isset
Check whether variables are defined

14. is_bool
Check whether the variable is Boolean

15. is_array
Checks whether the variable is an array.

16. is_object
Checks whether a variable is an object.

17. the substr () function returns part of the string.

Substr (String, Start, SelectNum)
The code is as follows:
Echo substr ('abcdef', 1); // bcdef
Echo substr ('abcdef', 1, 3); // bcd
Echo substr ('abcdef', 0, 4); // abcd
Echo substr ('abcdef', 0, 8); // abcdef
Echo substr ('abcdef',-1, 1); // f

18. nb2br () converts the escape line to html

The code is as follows:
Echo nl2br ("foo ISN'T \ n bar ");