The latest C language introduction and advanced - the most complete and detailed C language tutorial in history!! Section 1 - overview of C language

C Language introduction to advanced — Introduction section 1

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Start with this article , We are about to proceed systematically C Language introduction to advanced teaching , The outline is as follows ：

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Preface

From this section, we officially begin C Introduction to language learning

One 、 data type

The following are our common data types

Why are there so many data types ？ In fact, it is to express various values in life more abundantly .
for example ： We are describing age , We use an integer type for dates . When we describe weight , We often use floating-point numbers for PI and so on . Description letter , Use character type when writing characters .

1. The size of each data

All our data needs to be stored in memory , So how big is the data we often use ？

（1） At this time, let's learn about the various memory size units we often use

bit- bits
byte byte （1 Bytes equal to 8 bits ）
KB =1024 byte
MB=1024KB
GB=1024MB
TB=1024GB
PB=1024TB

(2) Built in function for calculating size sizeof（）

The calculation is as follows ：

Two 、 Variable constant

Some values in life are constant （ such as ： PI , Gender （ Generally speaking ） wait ）
Some values are variable （ such as ： Age , weight ）.

1. Variable

（1） How to define variables

The code is as follows （ Example ）：

	int age = 150;
	float weight = 45.5f;
	char ch = 'w';

（2） Classification of variables

#include <stdio.h>
int global = 2019;// Global variables 
int main()
{
    
    int local = 888;// local variable 
    int global = 2022;// local variable 
    printf("global = %d\n", global);
    return 0;
}
// The printed result is  2022

summary ：
When a local variable has the same name as a global variable , Local variables take precedence .

（3） The scope and life cycle of variables

Scope
Scope （scope） It's a programming concept , Generally speaking , The names used in a program are not always valid / You can use
Of
The scope of the code that defines the usability of the name is the scope of the name .

1. The scope of a local variable is the local scope of the variable .
2. The scope of global variables is the whole project .

Life cycle
The life cycle of a variable is the period between the creation of a variable and its destruction

1. The life cycle of a local variable is ： Enter the scope lifecycle begins , Out of scope life cycle ends .
2. The life cycle of global variables is ： The whole life cycle of the program .

2. Constant

C Constants in a language can be divided into the following categories ：

Literal constants
const Modified constant variable
#define Defined identifier constant
Enumeration constants

#include <stdio.h>

enum Sex
{
    
 MALE,
 FEMALE,
 SECRET
};
// In brackets MALE,FEMALE,SECRET It's an enumeration constant 
int main()
{
    
    // Literal constants demonstrate 
    3.14;// Literal constants 
    1000;// Literal constants 
    
    //const  Modified constant variable 
    const float pai = 3.14f;   // there pai yes const Modified constant variable 
    pai = 3.14;// It can't be modified directly ！
    
    //#define The identifier constant for   demonstration 
 #define MAX 100
    printf("max = %d\n", MAX);
    
    // Enumeration constants demonstrate 
    printf("%d\n", MALE);
    printf("%d\n", FEMALE);
    printf("%d\n", SECRET);
    // notes ： The default of enumeration constants is from 0 Start , Increase in descending order 1 Of 
        return 0;
}

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3、 ... and 、 character string Escape character

character string

“hello world\n”

This is made up of double quotation marks （Double Quote） A string of characters is called a string literal （String Literal）, Or abbreviated characters strand .
notes ： The end of a string is a \0 The escape character of . When calculating the length of a string \0 It's the end sign , Does not count as a string Content .

#include <stdio.h>
（ prominent '\0' Importance ）
int main()
{
    
    char arr1[] = "bit";  
    char arr2[] = {
    'b', 'i', 't'};
    char arr3[] = {
    'b', 'i', 't', '\0'};
    printf("%s\n", arr1);
    printf("%s\n", arr2);
    printf("%s\n", arr3);
    return 0;
}

There are two common ways to define strings ：

char arr[]=“”;
char arr[]={};
In the use of {} Definition time , We can think of it this way If we don't add the end sign artificially \0 Words ,printf Function will continuously print down in memory , Look for the end sign \0, So the second sentence will appear garbled . Out think join \0 outside , We artificially give to the front [] This purpose can also be achieved when the size is specified in

The size is ： Number of characters defined + One is reserved for \0 The location of

Escape character

Escape characters, as the name suggests, change meaning .

We found that it didn't print as expected , At this time, you need to use escape characters .

Escape character paraphrase
\? Use... When writing multiple consecutive question marks , Prevent them from being parsed into three letter words
\ ’ Used to represent character constants ’
\“ Double quotation marks used to represent the inside of a string
\ \ Used to indicate a backslash , Prevent it from being interpreted as an escape sequence character .
\a Warning characters , Beep
\b Back space
\f Paper in
\n Line break
\r enter
\t Horizontal tabs
\v Vertical tabs
\ddd ddd Express 1~3 Eight octal numbers .
\xdd dd Express 2 Hexadecimal numbers .

summary

for example ： That's what we're going to talk about today , This article simply introduces the data structure , Variable constant , character string , The basic content of escape characters .