当前位置:网站首页>Rough notes of C language (1)
Rough notes of C language (1)
2022-07-05 07:18:00 【After reading thousands of books, you can pick them up and put 】
C Language is a computer language —— The language of human and machine communication (c Language ,c++,JANA,Python)
Computers have to develop —— Early recognition is binary .
Computers are hardware , Electrify , Electricity Division , Positive and negative , Used in computers 0 Means negatively charged ,1 Indicates positive electricity , All computers can handle are electrical signals ,0,1 Such a signal , Binary language . So to run a program, you just need to give it a binary sequence .
At the beginning of a program, you need to type a large string of code, such as :100001110110
It's too hard to remember these , So people wonder if they can give a name to a program instruction represented by a piece of code
Such as 1000011——ADD( Mnemonic symbol )
In the future, just fight ADD Just fine , It knows or turns into 1000011.
And this mnemonic is assembly language .
In the later development, people wanted one sentence to represent many strings of code , There was also B Language ——C Language ,C++,……( High-level language )
C Language —— Early immaturity —— mature —— popular
Early immaturity : Each company has its own customized functions , So every company has its own customized functions , My house c Language can't pass in your compiler software , I can't pass in his compiler . Then international standards appeared .
ANSICC( The National Bureau of standards )——C89( Launched in 2013 )/C90 (89,90 be similar )
later ISO cognizance C89 For thorough International Standards .
C99/C11 It's not popular , Many compilers do not support , Only by the same standard can it become popular , In order to run in various compilers .
C Language is a process oriented computer programming language , And C++,JAVA, Object oriented programming languages such as , Its compiler mainly includes Clang、GCC、WIN-TC、SUBLIME、MSVC、Turbo C etc. .
first C Language program
.c—— Source file
.h—— The header file
Main
: The main function : Program entrance , The program from main The first line entry of the function , No addition main Function, it doesn't know which line to start with .
How many more ?
Also, there are too many entrances. It doesn't know where to start . So the main function has and only has one , It can't be without .
data type
To put A There is room for saving , Now let's apply for a space from the computer memory , Give Way ch Take the application and place the space name ch, To store characters A.
Common data types correspond to print symbols
%c// Print data types in character format ;
%d// Print integer decimal data types ;
%f// Print floating point numbers ;
%p// Print in the form of an address ;
%x// Print in hexadecimal data type ;
Why are there so many types ?
What is the size of each type ?
answer : The range of values is different , To reduce memory , The corresponding number corresponds to the type , Different space occupied .
C Language standards sizeof(long)>=sizeof(int)
The current operating system has developed to 64 Bit operating system , However, due to the different process of program compilation , The two show different differences :
32 Bit compiler system :int Four bytes , And long identical .
64 Bit compiler system :int Four bytes ,long Occupy 8 byte ,long The data range becomes :-263~263-1
Sizeof():
Calculation xx The amount of space taken up , Unit byte ;
Units in a computer
A computer is a piece of hardware , Electrify , It recognizes electrical signals , Positive and negative electricity Division , Positive for 1, Negative is 0, The electrical signal is converted into a signal that the computer can recognize 1 and 0. Computer can recognize positive and negative , Prove that it can recognize 1 and 0 Such a signal .
that 1 and 0, Such instructions need space to store , Deposit 1 or 0 Such a space size is a bit .( Store a binary bit ).
A byte 8 A bit ;
For example, there are three bits 23 There are two possibilities and the largest data is 23-1;
Sixteen bits have 216 There are two possibilities and the largest data is 216-1;
Report errors ,
float
It's single precision ,95.6 It is regarded as double precision
So sometimes in 95.6 After add f Just fine . But sometimes you can't just change .
Variable
Global variables : Defined in the code block ({}) Other variables ;
local variable : Defined in the code block ({}) The variables within ;
&: Address fetch , Tell him to put this input data here .
The computer memory is very large, so it is convenient to divide the memory into small pieces , Easy to find , For example, get the address directly num1;
Local variables can only be used in {} Use in ;
It is recommended that the names of local variables and global variables should not be the same . Easy to produce bug
When local variables and global variables exist at the same time, local variables have priority ;
The scope and life cycle of variables
Scope : The concept of programming , Generally speaking , The names used in a program are not always valid / Usable . The scope of the available code that limits the name is the scope of the name .
Scope of variable
:
- The scope of a local variable is the local scope of the variable ;
- The scope of global variables is the whole project ;
extern Declaration of external symbols
shazi, Put it in the code block {} Calculate the global variables ;
Life cycle :
The life cycle of a variable is the period between the creation of a variable and its destruction .
4. The life cycle of a local variable is : Enter the beginning of the scope lifecycle , Work or end of life cycle ;
5. The life cycle of global variables is : The whole life cycle of the program .
边栏推荐
- 能量守恒和打造能量缺口
- Unity ugui how to match and transform coordinates between different UI panels or uis
- What does soda ash do?
- Use of Pai platform
- Pytorch has been installed in anaconda, and pycharm normally runs code, but vs code displays no module named 'torch‘
- What is sodium hydroxide?
- DelayQueue延迟队列的使用和场景
- DataGrid offline installation of database driver
- And let's play dynamic proxy (extreme depth version)
- Mipi interface, DVP interface and CSI interface of camera
猜你喜欢
1290_ Implementation analysis of prvtaskistasksuspended() interface in FreeRTOS
HDU1232 畅通工程(并查集)
Pytorch has been installed in anaconda, and pycharm normally runs code, but vs code displays no module named 'torch‘
1290_FreeRTOS中prvTaskIsTaskSuspended()接口实现分析
window navicat连接阿里云服务器mysql步骤及常见问题
Brief description of inux camera (Mipi interface)
Steps and FAQs of connecting windows Navicat to Alibaba cloud server MySQL
Intelligent target detection 59 -- detailed explanation of pytoch focal loss and its implementation in yolov4
Tshydro tool
[node] NVM version management tool
随机推荐
网易To B,柔外刚中
[OBS] x264 Code: "buffer_size“
Ros2 - ros2 vs. ros1 (II)
第 2 章:小试牛刀,实现一个简单的Bean容器
Intelligent target detection 59 -- detailed explanation of pytoch focal loss and its implementation in yolov4
Netease to B, soft outside, hard in
SOC_ SD_ DATA_ FSM
Ros2 - node (VII)
PowerManagerService(一)— 初始化
Database SQL practice 3. Find the current salary details of the current leaders of each department and their corresponding department number Dept_ no
U-boot initialization and workflow analysis
Interpretation of the earliest sketches - image translation work sketchygan
ROS2——安装ROS2(三)
Ros2 - configuration development environment (V)
Reading literature sorting 20220104
IPage能正常显示数据,但是total一直等于0
mingling
postmessage通信
[software testing] 06 -- basic process of software testing
苏打粉是什么?