Principles, language, compilation, interpretation

Preface

          Study Principles and language of computer Content ！

One 、 Hardware and software

            Hardware ： Things that can be seen and touched , for example , mouse 、 keyboard 、 Monitor .
            Software ： Things that can't be seen or touched , for example , Programs installed on the computer ,qq And wechat .

Two 、 The three principles

1. Computers are essentially performing ：“ Input -> operation -> Output ” step , Most of what computers do is these three steps .
   for example , Enter information on the keyboard , Click the relevant buttons of some programs to calculate , And then on the screen result .
   for example , See a movie ： Search for （ Input ）-> Networking requests （ operation ）-> Show search results （ Output ）.
   Input 、 Operations and output operations are data .

2. A set of instructions and data is a program .
   Program ： The program is Instructions and data Set , Instructions are also a special kind of data .
   Instructions ： Do not participate in the operation , It's about controlling operations , An instruction is an order . Control how the computer inputs , operation , Output . Analogy work in which the leader gives you orders , Arrange a task , You are responsible for completing . Every line of code we write can be regarded as an instruction to the computer , Instructions can be combined .
   data ： It can be divided into two kinds , Input data and output data . No matter how complicated the program is , It is essentially a collection of data and instructions .

3. The information processed by the computer is all digital -> Binary system -> Data is stored in memory in binary form .
   written words , video , How to express colors in numbers ？
   Color ：RGB.
   written words ： You need to use numbers to represent the computer to understand , By character encoding .
   Computers only know numbers , That only needs to show the information as a number one A corresponding mapping table is not enough ？
   ASCII Code is to convert words into numbers recognized by computer .

3、 ... and 、 Computer language

Computer language is for both sides , One is Computer , The other is people , It is a connection between computer and human bridge .
Or the language is computer friendly , Or be friendly . Friendly to people is called High-level language , Computer friendly is called Low level language .

1. Low level language
   • machine language ： Machine language is also called native code , Is the native language of computer （0 and 1 Two programming languages written in binary numbers ）, Can be directly recognized by the computer , No additional translation is required , Computer friendly .
   • assembly language ： take 0 and 1 Put together data that contains specific instructions and give it a name , Use English letters to indicate , This kind of thing is called Mnemonic symbol .
2. High-level language

Four 、 Compilation and interpretation

clear ： Whether compiling or interpreting , It's all... In essence translate , Translation is to translate a program into another state . for example , Translate English into Chinese , Translate the source code of the program we wrote into the machine language that the computer can execute, that is, the form of binary （ The ultimate purpose of Translation ）, To complete the work .

1. compile
   It is to translate all source code into machine language at one time , Fast execution .
2. explain
   Not a one-time translation , When the program is executed , Translate the source code into machine language one by one , Slow execution .
3. difference
   compile ： After the program is compiled, another set of Storable Code for . for example ,java Compile and generate bytecode , Is storable .
   explain ： Explain and execute , Explain one thing and execute another , The process is Do not generate storable Code for
   summary ： compile When translating and executing Separate Of , and explain It is Sync On going

5、 ... and 、 Translation and execution

1. Translated Purpose ： Generate code in another format , take A become B The process of ,B Can be executed directly by the computer .
2. compile ： One step in place , Directly translate the source code into the target machine code （ machine language ）, It can run directly . The emphasis is on one-off , Translate the source code directly into machine code , If you want to run, you can directly read the run .
3. explain ：A become B,B It's not machine language , It cannot be directly executed by the computer , It belongs to a kind of intermediate code , It needs to be translated into target machine code again （ machine language ） To be executed by a computer . The process of retranslation is generally interpretation , The emphasis is to translate again , That is to translate one by one , Translate and execute .
4. perform ： The ultimate goal of execution is to run in the computer , To run, you need to perform the previous translation process .

5、 ... and 、 The two forms are combined

1. Compile implementation ： It is to translate the source program into the target machine code in one step , And then run directly .
2. Explain to perform ： Intermediate code to be generated , It's not the source program anymore , Then translate the intermediate code one by one into the target machine code , Translate one , To perform a , That is, execute while translating . for example ,java , The intermediate code is class file , Bytecode .
   java The original document ：xx.java, Generate intermediate code after compilation ：xx.class Bytecode file , It needs to be interpreted into the target machine code again for execution .

6、 ... and 、 compile

python First translate into intermediate code , Then give it to a specific ·python· The interpreter interprets and executes the generated object code , And then run .
c c++ It's a compiled language , Translate the source program at one time （ compile ） Into machine code , And then run .