Part I - Fundamentals of C language_ 1. Overview of C language

1.1 C Language

Language is communication between people ,C Language is the communication between man and machine .

Languages have unique grammatical rules and definitions , Programmers must follow these rules and definitions to communicate with computers .

1.1.1 Computer structure composition

  The computer is made up of three parts ： Input 、 processor 、 Output .

It is important to understand , The arithmetic unit reads data from the register 、 Register reads data from memory 、 Memory reads data from external storage .

1.1.2 Computer system composition

Just mix a familiar face here , Have a general understanding of what constitutes a computer system . Later, you will become familiar with these components .

1.2  Why study C Language

1.2.1 C Language features

1) advantage

1. Fast execution
2. Powerful
3. Programming Freedom

2) shortcoming

1. Writing code takes a long time
2. Poor portability
3. Rely more on platform libraries

1.2.2  Study C Language reasons

1.2.3 C Language applications

C Language is widely used , From the website background , The underlying operating system , From multimedia applications to large-scale online games , All can use C Language to develop ：

1. C Language can write website background program
2. C Language can write powerful program libraries for a specific topic
3. C Language can write the engine of large-scale games
4. C Language can write operating system and driver , And only use C Language writing
5. As long as any device is equipped with a microprocessor , All support C Language . From microwave ovens to mobile phones , It's all by C Language technology to promote

1.2.4 C What language needs to learn

C Language only 32 Key words ,9 Control statements ,34 Operator , But it can complete countless functions ：

Let's make a face , About how much to learn .

1.2.5 Study C Common confusion

1.3 first C Language program ：HelloWorld

1.3.1 To write C The language code ：hello.c

#include <stdio.h>

int main()
{
	printf("hello world\n");    // The first code 
	return 0;
}

stay VS Enter the above code on （VS The installation and preliminary use of... Should be carried out by yourself B Find a video on the station to learn , About half an hour to master ）.

1.3.2  The code analysis

1) include The header file contains

1. #include The header file contains ,#include <stdio.h> The representative contains stdio.h This header file
2. Use C The language library function needs to include the header file corresponding to the library function in advance , As used here printf() function , Need to include stdio.h The header file

#include< > And #include ""  The difference between ：

1. < >   The presentation system direct Search according to the directory specified by the system
2. ""     The presentation system First stay "" Specified path ( No written path represents the current path ) Find the header file , If you can't find it , Again Search according to the directory specified by the system

2) main function

1. A complete C Language program , Is written by a 、 And only one main() function ( Also called principal function , There has to be ) Combined with several other functions （ Optional ）.

     2. main The function is C The entrance to language programs , The program is from main The function starts executing .

3) {} Brackets , Program body and code block

1. {} It's called a code block , There can be one or more statements inside a code block
2. C Every sentence of executable code in the language is ";" End of semicolon
3. be-all # Beginning line , All represent precompiled instructions , There is no semicolon at the end of the precompiled instruction line
4. All executable statements must be in code blocks

4) notes

1. // Call line comment , The contents of comments are ignored by the compiler , The main function of comments is to add some descriptions and explanations to the code , This is good for reading the code
2. /**/ It's called a comment
3. Block annotation is C Language standard annotation method
4. The line comment is from C++ The language is borrowed from

5) printf function

1. printf yes C Library functions , The function is to output a string to the standard output device
2. printf(“hello world\n”);   \n It means to return to the bus for a new line

6) return sentence

1. return Represents that the function has been executed , return return Some values
2. If main The definition is preceded by int, that return Then you need to write an integer ; If main The definition is preceded by void, that return You don't need to write anything later
3. stay main Function return 0 Represents the successful execution of the program ,return -1 On behalf of program execution failure
4. int main() and void main() stay C It's the same in language , but C++ We only accept int main This way of defining

The above analysis of each part of the code can be understood first , As you continue to study in depth, you will naturally understand .

1.4 C Language compilation process

1.4.1 C Program compilation steps

C The code is compiled into an executable program after 4 Step ：

1. Preprocessing ： Macro definition expansion 、 Header file expansion 、 Conditional compilation, etc , At the same time, delete the comments in the code , There is no inspection here                 Check grammar （ Generate .i file ）
2. compile ：    Check grammar , Compile the preprocessed file to generate assembly file （ Generate .s file ）
3. assembly ：    Generating assembly file into object file （ Generate .o file ）
4. link ：   C Programs written in language need to rely on various libraries , So after compilation, you need to link the library to the final executable                   Go in the program （ Generate .exe file ）