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Preface ：
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Series index ：

Preface

Bo master slave 0 To begin C The analysis of language , Guide readers vividly c Language learning , Don't copy mechanically ！🧙‍*️🧙‍*️🧙

Everyone is happy to study together C！

One 、C Language program structure

1.1 Program structure

1. Any programming language has its own grammatical rules and prescribed expressions .
2. Computer programs can only be written in strict accordance with the grammar and expression specified by the computer language , In order to ensure that the written program can be correctly executed in the computer , It is also easy to understand and read .

The programs are all from main The function starts executing , Any program main Functions are indispensable , It is the entrance to the execution of our program

1.1.1 Basic constituent unit

1.C Language programs must have and can only have one main) function （ Also called principal function )
2. A complete C Language program , Is written by a main() Function and several other functions , Or just one main) Function constitution .

1.1.2 Start and end

One C Language program , Always from main() The function starts executing , Regardless of its position in the program . When the main function is completed , That is, the program is completed . Habitually , Main function main( Put it first .

1.1.3 Function composition

Any function is composed of function description and function body （ Include main function ）

Its general structure is as follows :
Function type function name ( Function parameter table ) → Function header
{
Data description section ; → The body of the function
Algorithm description ; → The body of the function
}
among : Data description . Used to define the variables used in this function ; The executable part , Complete specific functions , Consists of several statements .

1.2 Program writing format

• C Language statements must be semicolon “ ;” end .
• The writing format of the program line is free , It is allowed to write several statements in one line , It is also allowed to write a statement on several lines .
• “ Compact alignment , Automatic indentation ”
• Use the annotation function properly .C The annotation format of the language is :/*…*l
• The position of the note , It can occupy a single line , It can also follow the statement .
• Chinese characters are allowed in comments . Under non Chinese operating system , What I saw was a mess ,, But it does not affect the operation of the program .

Two 、 case analysis

2.1 Case a

Code block ：

#include <stdio.h>
void main()
{
    
int a,b,sum;
a=123;b=456;
sum=a+b;
printf("sum is %d\n",sum);
}

analysis ：

• First, add the compilation preprocessing command #include <stdio.h>（ Add this file to the current program ）
• Then write the main function
• The first line of the main function defines integer variables a,b,sum
• The second line of the main function is the setting a and b Value , That is the assignment
• The third line of the main function is to make sum=a+b
• The fourth line of the main function is the output character ：sum is xx（xx yes sum Value ）（%d Set integer output ）

On board test ：

stay devc Enter the above example :

The result is zero ：

2.2 Case 2

Code block ：

#include <stdio.h>
void main()
{
    
	int a,b,sum;
    a=10;
    b=24;
    sum=add(a,b);
    printf("sum= %d\n",sum);
}
int add(int x,int y)
{
    
	int z;
    z=x+y;
    return(z);
}

analysis ：

• First add stdio Function header file
• Then enter main Function
• to a,b,sum The definition of （int： integer ）
• And then assign it to a and b
• Then perform the sub function operation （ Here we use the call of sub functions ）
• Print sum Value
• The main function ends and enters the sub function definition
• add The function is used to input two values x and y Add and output
• Then the main function calls add The result of the function is to a and b Add the value to sum

On board test ：

stay devc Enter the above example :

The result is zero ：

summary

This article is the second chapter , Mainly to let everyone know C Language related programming rules . This chapter requires careful study ！

I think the most important thing to learn a programming language is to practice and think , We need to think more in daily life , Only by practicing more can we reach a certain height ！

come on. ! Ape friends ！