C deep anatomy - the concept of keywords and variables ＃ dry inventory ＃

1.

C In language 32 Key words C99 More 5 individual

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compiler ： Put text code -> Binary executable (exe file ), You can double-click to start the file , Generate executable file and run

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The essence of double clicking

Load program data into memory , Any program must be loaded into memory before being run

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The file was not run （ When not loaded ） Before , Where is the ？

On hard disk （ peripherals ） in

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Why load in memory ?

reason ： fast ！ because CPU Accessing memory is much faster than directly accessing input devices

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The von Neumann system

Input device input data, first put the data into memory , after CPU Calculation , Write the result back to memory after calculation , Refresh to the output device

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2. Keyword classification

• auto Declare automatic variables
• short Declare short integer variables or functions
• int Declare an integer variable or function
• long Declare long integer variables or functions
• float Declare floating-point variables or functions
• double Declare a double precision variable or function
• char Declare character type variables or functions
• struct Declare a structural variable or function
• union Declare shared data type
• enum Declare enumeration type
• typedef Used to alias data types
• const Declare read-only variable
• unsigned Declare an unsigned type variable or function
• signed Declare a symbolic type variable or function
• extern Declare variables are being declared in other files
• register Declare register variables
• static Declare static variables
• volatile Explain that variables can be implicitly changed during program execution
• void Declares that the function returns no value or takes no arguments , Declare no type pointer
• if Conditional statements
• else Conditional statement negates Branch （ And if Continuous use ）
• switch For switch statements
• case Switch statement Branch
• for A circular statement
• do The body of a loop statement
• while The loop condition of a loop statement
• goto Jump statements without conditions
  continue End the current cycle , Start next cycle
• break Jump out of current loop
• default In the switch statement “ other ” Branch
• sizeof Calculate the data type length
• return Subroutine return statement （ With parameters , Or without parameters ） The loop condition

3. Definitions and statements

Definition ： Make room in memory ( There can only be one time ), To hold data

Statement ： inform （ It can be stated many times ）

3.1. What is a variable

Log in and copy

 Open up a specific size of space in memory , To hold data 

     

      
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