Summary of commonly used special operation symbols and functions in PHP

Annotation symbols:
// Single-line annotation
Multi-line annotation
Use of quotation marks
' ' Single quotation marks, simple strings, taken directly without any processing;
" "Double quotation marks, PHP dynamic processing and then output, generally used Process $variables.
Boolean variables:
One is true, which is true;
The other is false, which is false.
Common variables:
string string (digits, Chinese characters, etc.)
integer integer (1, 2, 3, 4, 5, 0, -1, -2, etc.)
double floating point number (decimal point)
array array
object object
The methods that can be used are gettype($mix) and settype($mix,$typename);

Commonly used symbol escapes:
" double quotes
\ backslash
n newline
r return to the beginning of the line
t horizontal tab
Arithmetic symbols:
+ addition operation - subtraction operation
* multiplication operation/division operation
% take the remainder ++ Increment by 1
-- Decrement by 1. Connect two strings
Assignment operation:
= Substitute the value on the right into the left
+= Add the value on the right to the left
-= Subtract 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
Bit operations:
& Bitwise AND
| Bitwise OR
^ Bitwise XOR (xor)
>> Shift 1 bit to the right
~ Complement
Logical operation:
Greater than
= Greater than or equal to
!= is not equal to && and
|| or! Other operation symbols than

$ variable symbols
& aliases for variables
@ does not display error messages (added before functions)
-> methods or attributes of objects
=> ; Element value of array
?: Ternary operator

Commonly used basic methods:

1.PHP converts strings to uppercase and lowercase!

strtolower(); Convert characters to lowercase
strtoupper(); Convert characters to uppercase

2.PHP encrypted string

Irreducible:
md5();
sha1();
Reducible:
base64_encode();
base64_decode();

3. About quotation marks

1. Single quotation marks are as they are Output
2. Double quotation marks are for content interpretation and output
3. Anti-single quotation marks (small quotation marks) are used to execute a system command, such as `dir`.
4. "" is used for translation characters. , such as "n" is a newline.

4. Functions: htmlspecialchars() and htmlentities()
This function may be used to convert special characters into HTML string format (&....;). The message board for customer messages has been processed.

& (and) is converted to &
" (double quotation marks) is converted to "
> (greater than) is converted to >
(space) is converted to

5. Batch output HTML content!

echo HTML output content. . . //Comments here are still output!
EOT;

print HTML output content. . . //Comments here are still output!
EOT;
(Note: Use "{variable}" for internally included variables)

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

<?php
$FileName="File.TXT";
if (file_exists($FileName)){
echo "<pre class="brush:php;toolbar:false">".file_get_contents($FileName)."

"; }else { echo"no"; } ?>

7. Delete variables to release memory unset();

unset($var );
unset($var,$var1);

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

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

10.is_null;
Detect whether the variable is NULL ;

11.is_string
Detect whether the variable is a string

12.is_real;
An alias of is_float()

13.isset
Detect whether the variable is defined

14.is_bool
Detect whether the variable is a Boolean type

15 .is_array
Detects whether the variable is an array

16.is_object
Detects whether the variable is an object

17.substr() function returns a 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() turns the escaped newline into html

. The code is as follows:

echo nl2br("foo isn'tn bar");