Programming language (1)

Preface ：

What is a program ？

• The program is for A sequence of instructions written in a programming language to solve a problem with a computer
• notes ： Procedure is ： Sequence of commands . error . because ： Commands are not necessarily understood and executed by computers .

What is a programming language ？

• Programming languages are used for communication between people and computers （ communication ）
• Programming language is a language that is used by people but understood by computers
• Programming language be used for Programming , Express what task the computer needs to complete and how to complete the task , Then give it to the computer to complete

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  One 、 machine language

• Machine language is the instruction system of computer
• Instructions are expressed in binary code
• Program in machine language , That is to write programs directly using binary code
• advantage ：

1. Sure Directly executed by the computer

• shortcoming ：

1. Can't remember 、 Hard to understand 、 Low efficiency 、 Difficult to maintain
2. Different machine language programs , Not compatible with each other
3. Not portable .

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  Two 、 assembly language （ Semiotic language ）

use Mnemonic symbols to indicate machine instructions Medium Operators and operands

advantage ：

• machine language 、 Assembly language can directly operate hardware

shortcoming ：

• Machine oriented language . Poor portability

  A summary of machine language and assembly language

• What is machine language ？ Namely CPU The command system of . It's a binary number . It is the only directly executable language of hardware . It's not portable .（ This is because of different machines CPU Different instruction systems , So machine languages are different .） The program written in machine language is called ： Executable program .
• What is assembly language ？ Is symbolic language . Almost directly corresponds to binary machine instructions . The program written in assembly language is called ： Assembly language source . Not directly .（ You have to pass the assembler first ( A system software ), Assemble the whole assembly language source program into machine language executable program , And then we can execute .） It's also Not portable .（ This is because it almost directly corresponds to binary machine instructions , And different CPU, Its instruction system is usually different . So it's not portable .）
•             notes ： ask ： The programs written in machine language are all system software . error . Machine language can write any software （ Not necessarily system software ）.

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  3、 ... and 、 High level programming language

• Purpose ： Overcome the defects of assembly language , Improve the efficiency of programming and maintenance
• characteristic ：

1. Close to the natural language that people use everyday （ Mainly English ） Easy to understand 、 Memory and use
2. It can be used on different computers . Strong portability
3. For the symbols used 、 vocabulary 、 Grammar, semantics and other language components are strictly regulated

• significance ： Reduce the difficulty of program design , Led to the development of computers into a new stage
• shortcoming ： Computer Not directly perform

Namely Human oriented language （ Machine language and assembly language are machine oriented languages ）. The program written in high-level language is portable （ This is because it is far away from the machine , Not facing the machine , Therefore, the level of abstraction is high ）, but Not directly executable .

（ One ） Elements of high-level programming language —— data 、 operation 、 Control and transmission

1. Data components
2. Arithmetic component
3. Control ingredients
4. Transmission components

（ Two ） The control structure of the program —— The order 、 choice 、 Cycling and modularity

（1） Sequential structure —— Execute according to the sequence of statements

（2） Selection structure —— Single branch 、 Two branches and many branches

1. Single branch

if sentence

2. Double branch

if-else sentence

 

 3. Multiple branches

if-elif-else sentence

（3） Loop structure ——while sentence 、do while Statement and for sentence

（ Four ） modularization

• The source program is divided into modules
• Module corresponding function
• Program = The main function + Subfunctions