How is the plus sign represented in binary?
Check the ascii code list to know that 43 stands for + binary 101011
http://ke..com/link?url= DsujKIpzxRiczNo2pwIti9oMir6IQkYCqb1hxmo3natx7kCZNtLU8TEYBzay2sLFSV8VTfeZGaxY0-FyqOKq7fjVO1o1NSMmhX70XMHi8vaQ-f2lc68VNLwE3-5bktP1
What is the URL format
In the WWW, each information resource has a unified and unique address on the web, the address is called the URL (UniformResourceLocator, Uniform Resource Locator), which is a unified resource locator mark of the WWW, that is, the network address.
The URL consists of three parts: the type of resource, the host domain name of the resource, the resource file name. It can also be considered to be composed of four parts: protocol, host, port, and path.
Main parts of URL syntax:
The fifth part gives a complete BNF description of the URL syntax.
URLs are usually written in the following form: <scheme>:<scheme description part>
A URL contains the name of the scheme it uses (<scheme>), immediately followed by a colon, and then a string (<scheme description part>), which is interpreted as determined by the scheme used. determine.
The program name consists of a string of characters. lowercase letters “a” – “z”, numbers, the character plus (“+”), periods ( “.”) and hyphen (“-“) are all allowed. For convenience, the program should interpret the URL as if it were an uppercase letter as well as a lowercase letter in the scheme name. (e.g., treat “HTTP” as the same as “http”).
What are the single punctuation marks of HTML
Punctuation marks. Any C program is made up of symbols from C’s symbol set that form statements with certain meanings, which in turn form the program.
I. Letters, numbers, and underscores
Upper case letters: A–Z
Lower case letters: a–z
Numeric symbols: 0– -9
Underline: _
Two, blank characters
Blank characters are: space, tab, vertical tab, carriage return, line feed, page break. In the C source program only produces a “blank” role. The blank character only works in character constants and string constants. When they appear elsewhere, they only act as spacers and are ignored by the compiler. Therefore, the use of whitespace in a program does not affect the compilation of the program, but the use of whitespace in appropriate places in the program will increase the clarity and readability of the program.
Three, punctuation and special symbols
Punctuation and special symbols used in C
Symbol name Symbol name
, comma > right pointed bracket
. Dot! exclamation point
; semicolon|vertical line
: colon/slash
? question mark\backslash
‘single quotes ~ dash
“double quotes # wells
(left parentheses % percent sign
)right parentheses &and (with)
[left square bracket ^xor (iso or)
]right square bracket *multiply
{left curly bracket-minus
}right curly bracket=equal
<left pointed bracket+plus
Fourth, escape characters
Endorsed characters are a special form of representing characters in C language. Usually use escape characters to indicate the ASCII character set in the non-printable control characters and specific functions of the characters, such as single apostrophe (‘) used to indicate the character constants, double apostrophe (“) used to indicate the string constants and backslashes (\) and so on. Escape characters are represented by a backslash \ followed by a character or an octal or hexadecimal number. Table 2-4 gives the commonly used escape characters in C.
Table 2-4 Escape Characters
Endorsement Character Meaning ASCII Code Value (Decimal)
\a Ringing Bell (BEL) 007
\b Backspace (BS) 008
\f Page Feed (FF) 012
\n Line Feed (LF) 010
\r Carriage Return (CR) 013
\t Horizontal Tab (HT) 009
\v Vertical Tab (VT) 011
\\\\\backslash 092
\? Question mark character 063
\’Single quote character 039
\”Double quote character 034
\0 Empty character (NULL) 000
\ddd arbitrary character three-digit octal
\xhh arbitrary character two-digit hexadecimal
The role of the escape character: to represent control codes; to represent characters and string constants; indicates any character in the ASCII character set.
The use of single quotes and backslashes in character constants as well as the use of double quotes and backslashes in character constants must be represented by escape characters, i.e., backslashes in front of these characters.
Using the escape characters \ddd or \xhh in a C program makes it easy and flexible to represent arbitrary characters. \ddd is a slash followed by three octal digits, the value of the three octal digits is the corresponding octal ASCII value. \x followed by two hexadecimal digits, the two hexadecimal digits for the corresponding character hexadecimal ASCII code value.
When using escape characters, you need to pay attention to the following issues:
1) Only lowercase letters can be used in escape characters, and each escape character can only be regarded as one character.
2)\v Vertical tabs and \f page breaks do not have any effect on the screen, but they do affect the printer’s ability to perform response operations.
3)In C programs, when non-printable characters are used, they are usually represented by escape characters.
V. Naming of Identifiers
In C, identifiers name variables, functions, labels, and various other user-defined objects.
1. Characters used
Must use English letters, numbers and underscores from the C symbol set.
2, length
ANSI standard specifies that the length of the identifier is 1-32 letters, but the computer, the length of the identifier is only the first 8 characters uniquely distinguishable, more than 8 characters after the character is ignored. The following will be treated as the same identifier: counters, counters1, counters2.
3. Naming rules
The length of an identifier can be one or more characters. In the vast majority of cases, the first character of an identifier must be a letter or an underscore, and subsequent characters must be letters, numbers, or underscores. Here are some examples of correct or incorrect identifier naming.
Correct formError form
count2count
test23hi!there
high_balancehigh…balance
Letters in C are case-sensitive, so countCountCOUNT is three different identifiers. The identifiers cannot be the same as C keywords, nor can they have the same name as a function already prepared by the user or a C library function.
VI. Keywords
Keywords are strings of characters with specific meanings specified by the C language, often called reserved words. User-defined identifiers should not be the same as the keyword.C language keywords are divided into the following categories: (1) type specifier: used to define, specify the type of variable, function or other data structure. Such as int, double, etc.. (2) statement definer: used to indicate the function of a statement. Such as ifelse is the conditional statement statement definer. (3) preprocessing command word: used to indicate a preprocessing command. For example, include is used in the previous examples.
The following table lists 32 keywords, which, in combination with standard C syntax, form the programming language C.
autobreakcasecharconstcontinuedefaultdo
doubleelseenumexternfloatforgotoif
intlongregistershortsignedsizeofstaticreturn
structswitchtypedefunionunsignedvoidvolatilewhile
Operator symbols:
-(minus or subtract), +(add), *(multiply), /(divide), %(take the remainder), –(minus 1), ++(plus 1)
Relational comparison symbols:
>(greater than), <(less than), >=(greater than equals), <=(less than equals), ==(equals), ! = (not equal to)
Logical operation symbols:
&&(and), ||(or), ! (inverse)
Bitwise operation symbols:
<<Shift one bit to the left >>Shift one bit to the right &(and), |(or), ~(inverse), ^(mutually exclusive)
Other symbols:
//**/Note symbols
=Specified symbols
:Narrative separator
*Indicator symbol
()Symbol for the beginning and end of an equation or argument column
[]Symbol for the beginning and end of an array of annotations
, used to separate the items of a column
\Controls the start of the formatting or chaining of symbols
#Front-end processing symbols
”Symbol for the beginning and end of the element
”Symbol for the beginning and end of an element
”Symbol for the beginning and end of an element
”’. symbols
”Symbols for the start and end of a string
? :conditional operator
&address symbol
%Controls the leading symbols of the output into the data format
–Copy of the
c language, output a number, such as 10, press the plus sign on the keyboard, 10 will be added one to 11, and then press again and add one, how to write such a program
#include <string.h>
#include <stdlib.h>
void main( a++;
else if(quit==’-‘) a–;
else{}
}while(quit!=’q’);
}
What is url encoding %3f?
Special Character Escape Encoding in URLs
Character-URL Encoding Values
Space-%20
“-%22
#-%23
%-%25
&-%26
(-%28
)-%29
+-%2B
,-%2C
/-%2F
:-%3A
;-%3B
<-%3C
=-%3D
>-%3E
? -%3F
@-%40
\-%5C
|-%7C
URL Special Character Escaping
Special Meaning of Some Characters in the URL, the basic coding rules are as follows:
1, space is replaced with a plus sign (+)
2, a forward slash (/) separates the directory and subdirectory
3, question mark (?) Separate URLs and queries
4, percent sign (%) to develop special characters
5, # sign to specify the bookmark
6, & No. Separate parameters
If you need to use in the URL, you need to change these special characters to the corresponding hexadecimal value
+%2B
/%2F
? %3F
%%25
#%23
&%26
Because in the project often have to use AJAX to pass SQL to the backend server
Will encounter selectnum+1fromal or left and right connection form. Always lose (+)
This time you can try to use a little URL special character escaping
With JS’s encodeURI () function or directly change the value to the corresponding hexadecimal