An example Analysis of the literal amount of C # Grammar text 03/29 Update SLTechnology News&Howtos

An example Analysis of the literal amount of C # Grammar text

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Literal amount of C # grammar text

In daily life, text is used to represent content other than numbers. For example, there is a man named "Bill" whose position is "section chief". Then, both "Bill" and "Section Chief" can be called texts. In computers, real-world text is often called characters and strings. For example, every Chinese character in Bill is a character. And the whole makes up a string. The same is true of the section chief.

Writing specifications for characters and strings

What we see above is the common literal amount of text. However, in many cases, digital content does not necessarily express numerical values. For example, Bill's phone number is 13466668888. For "13466668888", we will not understand it as 13.466 billion 6668888, but as a telephone number. Due to the limited ability of the computer, in order to avoid this kind of information causing trouble to the computer, the program has the following provisions on the representation of characters and strings:

A character is a single letter, number, word, or symbol enclosed in single quotes (').

A string can represent a sequence of characters.

The string uses a pair of double quotation marks (") to combine with multiple characters.

There can be any number of characters in double quotation marks of a string.

According to this specification, if you want to represent the letter an in the program, it needs to be written as'a'. A character can contain only one character, so the character'a' is 1 in length. If you want to represent Bill's phone number in the program, it must be written as "13466668888". The length of the string is 11 because it contains 11 characters, and double quotes are string format symbols and cannot be counted as string lengths.

Special characters and strings-escape characters

Sometimes you need to use special characters in a string, such as the string abc "s. The string" abc "s" in the code produces an error and the compiler cannot recognize the specific contents of the string. To solve this problem, you need to use escape characters. Escape characters represent some special characters by combining a backslash "\" with ordinary characters. The escape character contains at least two characters, the first character is the escape symbol "\", and the second character is the character to be represented. There are two commonly used escape characters: escape characters that represent formats and escape characters that represent control codes.

1. Presentation format

To form characters and strings, double quotation marks (") and single quotation marks (') are used. in order to form an escaped character, a backslash (\) is used. if you need to include these three characters in a string, you need to use escape characters as shown in Table 1.1.

Table 1.1 shows the list of escaped characters in the format

\ "

[example 1-4] has the following text content, which needs to be represented by a string in the program.

I love C#.

I am studying Che.

In this text content, the first line is expressed as a string of "I love clocking.", which is 10 in length (spaces vs.. All count as one character). The second line has a single quotation mark, so you need to use an escape character to express it as "I\ m studying clocking." the string is 16 in length.

2. Represents the control code

In the text data, there will be some special symbols, such as newline characters, backspace and so on. These symbols are not visible, but are used to control the formatting of the text. Since such characters cannot be written, they must be represented by escape characters as shown in Table 1.2.

Table 1.2 represents the escape character sequence of the control code

\ a

\ b

\ f

\ n

\ r

\ t

\ v

In example 1-4, because the two text contents are not on the same line, there must be a "\ n" between them to indicate a line break. Therefore, the correct representation of the two texts is "I love centering.\ n I\'m studying caching." the length of this string is 27.

A more comprehensive expression-- ASCII table

Escaping characters can solve most of the character expressions. However, there are still many characters that cannot be written directly, and there are no corresponding escape characters. At this point, you can only use ASCII to express it. ASCII is a computer coding system based on the Latin alphabet (26 English letters). It is now the most commonly used single-byte coding system. The format of the characters represented by ASCII is shown in Table 1.3.

Table 1.3 characters represented by ASCII

\ 0

\ ddd

Any character represented by a 3-digit octal number

\ xhh

Any character represented by a 2-bit hexadecimal number

In Table 1.3, any character represented by an octal number can be represented by octal, that is, the total length of such escaped characters is 2x4. When using hexadecimal characters, you can represent any character represented by a 1-bit 2-bit hexadecimal number, that is, the total length of this type of escape character is 3-4, because the "\ x" begins with the hexadecimal number.

[example 1-5] escape characters are used in the following code:

'\ x2f'

'\ 013'

Where\ x indicates that the following characters are hexadecimal numbers, and\ 0 means that the following characters are octal numbers.

For a more comprehensive representation, the character 0x127 of the ASCII table is given here. The details are shown in Table 1.4.

Table 1.4 ASCII table

[space]

ninety-eight

sixty-two

three

thirty-five

twenty-three

sixty-seven

forty-three

ninety-nine

sixty-three

four

thirty-six

twenty-four

sixty-eight

forty-four

one hundred

sixty-four

five

thirty-seven

twenty-five

sixty-nine

forty-five

one hundred and one

sixty-five

six

thirty-eight

twenty-six

seventy

forty-six

one hundred and two

sixty-six

seven

thirty-nine

twenty-seven

seventy-one

forty-seven

one hundred and three

sixty-seven

eight

\ b

forty

twenty-eight

(

seventy-two

forty-eight

one hundred and four

sixty-eight

nine

\ t

forty-one

twenty-nine

)

seventy-three

forty-nine

one hundred and five

sixty-nine

ten

\ r

forty-two

seventy-four

one hundred and six

eleven

forty-three

seventy-five

one hundred and seven

twelve

forty-four

seventy-six

one hundred and eight

thirteen

\ n

forty-five

seventy-seven

one hundred and nine

fourteen

forty-six

seventy-eight

one hundred and ten

fifteen

forty-seven

seventy-nine

one hundred and eleven

sixteen

ten

forty-eight

thirty

eighty

fifty

one hundred and twelve

seventy

seventeen

eleven

forty-nine

thirty-one

one

eighty-one

fifty-one

one hundred and thirteen

seventy-one

eighteen

twelve

fifty

thirty-two

two

eighty-two

fifty-two

one hundred and fourteen

seventy-two

nineteen

thirteen

fifty-one

thirty-three

three

eighty-three

fifty-three

one hundred and fifteen

seventy-three

twenty

fourteen

fifty-two

thirty-four

four

eighty-four

fifty-four

one hundred and sixteen

seventy-four

twenty-one

fifteen

fifty-three

thirty-five

five

eighty-five

fifty-five

one hundred and seventeen

seventy-five

twenty-two

sixteen

fifty-four

thirty-six

six

eighty-six

fifty-six

one hundred and eighteen

seventy-six

twenty-three

seventeen

fifty-five

thirty-seven

seven

eighty-seven

fifty-seven

one hundred and nineteen

seventy-seven

twenty-four

eighteen

fifty-six

thirty-eight

eight

eighty-eight

fifty-eight

one hundred and twenty

seventy-eight

twenty-five

nineteen

fifty-seven

thirty-nine

nine

eighty-nine

fifty-nine

one hundred and twenty one

seventy-nine

twenty-six

fifty-eight

ninety

one hundred and twenty two

twenty-seven

fifty-nine

ninety-one

[

one hundred and twenty three

{

twenty-eight

sixty

ninety-four

one hundred and twenty six

thirty-one

sixty-three

ninety-five

one hundred and twenty seven

Many of the characters in Table 1.4 cannot be displayed, so they are displayed in white space. In coding, characters can be used by combining a backslash "\" with the hexadecimal number of ASCII characters. For example, "\ n" and "\ 0D" play the same role. But most characters can be output directly, and you don't need to use this way.

Avoid escaping characters-- @

In programming, sometimes the combination of characters happens to be the same as the escape character, and it is necessary to invalidate the escape character in that combination. There is a special character "@" in C # that declares the literal string and ignores the escape character.

[example 1-6] if you want to represent an address "c:\ temp". When we output "c:\ temp" in the code, the result is shown as follows:

C: emp

Why is such a result displayed? Because in "c:\ temp", the "\ t" in the string is recognized by the computer as an escaped character, it acts as a horizontal tab. In this case, you can use the escape character "\" to output the backslash so that the string represents an address as follows:

"c:\\ temp"

This representation can temporarily solve the simple address in front of you. However, this kind of writing can be very cumbersome if the address you want to represent is long and complex and contains multiple backslashes. For example, when the address to be represented is "c:\ temp\ 1\ t\ 3\ a\ 5", it is expressed in this way as:

"c:\\ temp\\ 1\ t\ 3\ a\\ 5"

The above expression is very tedious and prone to writing mistakes. Therefore, you can use the special symbol @ to mask the role of escape characters. When we want to represent the address "c:\ temp\ 1\ t\ 3\ a\ 5", we just need to precede the address with the special character @, as follows:

@ "c:\ temp\ 1\ t\ 3\ a\ 5"

String length

Above, we learned about characters, strings, escape characters, and so on, and then we learned their respective character lengths. The types, examples, length, and output of various characters and strings are shown in Table 1.5:

Table 1.5 string length

/ string example

'a'

one

"abc"

three

Abc

"ab\"

four

Ab'c

"ab\ nc"

four

String represented by ASCII

"ab\ x22"

three

Ab "

@ string

@ "ab\ x22"

Ab\ x22

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