What are the differences between c and javascript

Difference: 1. C language requires manual memory management, while JavaScript memory is managed by the interpreter; 2. C language is a statically typed language, while JavaScript is a dynamically typed language; 3. There are Closures are not available in C language; 4. C language is a compiled language, while JavaScript is an interpreted language.

The operating environment of this tutorial: windows7 system, javascript1.8.5&&c99 version, Dell G3 computer.

The difference between C language and JavaScript

1. C language requires programmers to manually manage memory (mainly referring to the application and release of heap memory), while JavaScript’s memory is Managed by the interpreter;

2. C language is a statically typed language, that is, the data type of each variable is determined before the program is run and cannot be changed during runtime, while JavaScript is a dynamically typed language. Language, the data type of variables can still change during runtime;

3. There is no concept of closure in C language, and functions in JavaScript form closures with variables that are accessible when they are defined;

4. C language can implement multi-threading by calling the system API, and can use multi-threading to improve the CPU utilization during blocking operations (mainly IO), while JavaScript is mainly single-threaded, and all operations that may block in JavaScript are This is done by the asynchronous API provided by the JavaScript runtime.

5. C language is a compiled language, while JavaScript is an interpreted language. C language is mainly compiled into machine language, while JavaScript is mainly interpreted and executed as a script by the interpreter;

From the perspective of static type or dynamic type

• Static type, you can know the type of each variable when compiling, and you also need to give a given type when programming, such as integer type int, floating point type float, etc. in Java. C, C, and Java are all statically typed languages.

• Dynamic type, the type of each variable is only known when running. There is no need to display the specified type when programming, such as var in JavaScript and $ in PHP. JavaScript, Ruby, and Python are all dynamically typed languages.

• Static typing or dynamic typing has a great impact on the performance of the language.

• For static types, after compilation, the advantages of known types will be used extensively. For example, the int type takes up 4 bytes. The compiled code can use the memory address plus offset. Variables are accessed using quantitative methods, and the algorithm assembly of address plus offset is easy to implement.

• For dynamic types, they will be saved as strings, and string matching will be used for subsequent access.

From a compiled or interpreted perspective

• Compiled languages, like C and C, require a compiler It can only be run after being compiled into a local executable program, which is manually implemented by the developer after the writing is completed. Users only use these compiled local codes, which are executed by the system loader and directly executed by the CPU of the operating system without the need for other additional virtual machines.

  Source code=》Abstract syntax tree=》Intermediate representation=》Local code

• Interpreted languages, such as JavaScript and Python, write the code directly after the development language is written It is handed over to the user, who uses the script interpreter to interpret and execute the script file. For scripting languages, there is no developer compilation process, of course, not absolutely.

  Source code=》Abstract syntax tree=》Interpreter interpretation and execution.

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