keywords, identifiers, comments

first, the key word 1. What is a keyword

1> keyword is the C language provides a special meaning of the symbol, also known as "reserved word"

The 2> C language provides a total of 32 keywords, all of which are given special meaning by C language

Auto double int struct break else long switch

Case enum Register typedef char extern return Union

const float Short unsigned continue for signed void

Default goto sizeof volatile do if and static

2, the characteristics of the key words

1> are all lowercase

2> displays special colors in the development tool or in the Smart Text Editing tool. By default, all keywords in the C language are shown in Xcode with a violet-brown

3. What are the key words in the main function

int, return

Second, identifiers 1. What is an identifier

Identifiers are some of the symbols and names that you customize in your program. To differentiate from keywords: the keyword is the symbol that is provided by the C language by default, and the identifier is a programmer-defined

2, the role of identifiers

1) identifiers, literally understood, are symbols used to identify something, the purpose of which is to separate it from the other.

2) In fact, the function of the identifier is similar to the human name, in order to distinguish each person, at the time of each person's birth a name

3) C language is composed of functions, a C program may have more than one function, in order to distinguish these functions, each function is given a name. The name of the function is one of the identifiers. In addition to the function, the concept of "variable" will be learned later, and the name of the variable is also the identifier

3. Naming

1> naming rules (be sure to follow)

Can only be made up of 26 letters in uppercase and lowercase, 10 Arabic numerals 0~9, underline _

Strictly case-sensitive, such as test and test are 2 different identifiers

Cannot start with a number

You cannot use a keyword as an identifier

2> naming conventions (best to follow)

Try to make a meaningful name, such as a complete English word, which can be useful if someone sees the name. If you do not understand English, you can also use pinyin, try not to be like ABCDE, SFSDFSDF and other such seemingly meaningless names

If the identifier contains more than one word, you can use the Hump logo (except for the first word, the first letter of each word is capitalized): FirstName, MyFirstName, or use the underscore _ to connect: first_name, My_first_name

4. Common identifier naming error

Legal identifiers	Illegal identifiers	Comments
FromNo12	From#12	The # symbol cannot be used in identifiers
My_boolean	My-boolean	The "-" symbol cannot be used in identifiers, and the underscore "_" should be used instead
Obj2	2ndObj	Identifiers cannot start with numbers
MyInt	Int	"Int" is the built-in keyword
Jack_rose	Jack&rose	Symbol ' & ' cannot appear in the identifier
Gui	G.u.i	The identifier must appear inside the "." Separator

Third, comments 1. What is a comment

1) Annotations are a concept that is very important in all computer languages, literally, the meaning of annotations and explanations.

2) Comments can be used to explain the meaning of a program or a line of code to facilitate communication between programmers. If I finish writing a line of code and add the corresponding comment, then people will see this comment and know what my line of code is for.

3) Comments can be any text, which means you can write Chinese

4) Note in development tools is generally red bean paste Green

2. Single-line Comment

1) The single-line comment starts with two forward slashes, that is, starts with//, can only comment one line, from//start to the end of this line is the contents of the comment

2) anywhere you can write a comment: Outside the function, inside, behind each statement

3, multi-line Comment

Multiline comments start with/*, end with */, the contents of/* and/* are commented

4, the role of annotations

1> Annotated code does not participate in compilation

A note is written to people, not to a computer. How can a computer see the Chinese we write? Therefore, when compiling the program, the comments are not compiled into the. O Destination file

From the size of the. o file, you can see indirectly that the code after the comment has not been compiled

2> checking the role of code

3> Troubleshooting Errors

5. Nested phenomena of annotations

1) Single-line comments can be nested single-line comments, multiline comments

wow haha//Oh OH

/* FSDFSDF *//SDFSDFSD

2) multiline annotations can nest single-line comments

/*

Description: First C language Program

*/

3) Multiline comments cannot nest multiple lines of comments

/* ha ha haha

*/Hee Hee * *

Oh, OH *

4) The following wording is wrong

// /*

Ha ha haha

*/

keywords, identifiers, comments