Understanding Computer Ⅳ:

Introduction to Computer Programming Languages

Programming languages are the foundation of software development, enabling humans to communicate with computers and create a wide range of applications. In this article, we will explore the world of programming languages in detail, covering their history, classification, and popular examples.

History of Programming Languages
Classification of Programming Languages
1. High-Level vs Low-Level
2. Imperative vs Declarative
3. Compiled vs Interpreted
Popular Programming Languages
1. Python
2. JavaScript
3. Java
4. C++
5. C#
Conclusion

1. History of Programming Languages

The history of programming languages dates back to the 1940s, starting with assembly languages and early high-level languages. Since then, the field has evolved significantly, with new languages being developed to better suit various programming paradigms and application domains.

1940s: Assembly languages
1950s: Early high-level languages (e.g., Fortran, COBOL, LISP)
1960s: Development of ALGOL, which influenced later languages such as Pascal, C, and Simula
1970s: Emergence of C, Pascal, and Smalltalk
1980s: Development of C++, Objective-C, and Ada
1990s: Introduction of Java, Python, and Ruby
2000s: C#, Swift, Go, and Rust

2. Classification of Programming Languages

Programming languages can be classified based on various criteria, such as their level of abstraction, programming paradigm, and execution model.

2.1 High-Level vs Low-Level

High-level languages provide a higher level of abstraction from the hardware, making them more human-readable and easier to write and maintain. Examples include Python, JavaScript, and Java.

Low-level languages are closer to machine code, providing more control over the hardware but sacrificing ease of use. Assembly language is an example of low-level languages.

2.2 Imperative vs Declarative

Imperative languages focus on describing the step-by-step process to achieve a result. They often include loops and variables to control the flow of execution. Examples include C, Java, and Python.

Declarative languages express the desired result without specifying the steps to achieve it. They are often used for database querying or logic programming. Examples include SQL, Haskell, and Prolog.

2.3 Compiled vs Interpreted

Compiled languages require source code to be translated into machine code before execution. This process, called compilation, results in faster execution but can be time-consuming during development. Examples include C, C++, and Java.

Interpreted languages do not require compilation. Instead, the source code is read and executed line-by-line by an interpreter, which can lead to slower execution but faster development times. Examples include Python, JavaScript, and Ruby.

3. Popular Programming Languages

3.1 Python

Python is a high-level, interpreted, general-purpose programming language that emphasizes code readability and simplicity. It supports multiple programming paradigms, including procedural, object-oriented, and functional programming. Python is widely used in web development, data analysis, artificial intelligence, and more.

Example: HelloWorld.py

print("Hello World!")

print(): This is a built-in Python function that is used to display output on the screen.
"Hello World!": This is the message that will be displayed on the screen. It is enclosed in double quotes to indicate that it is a string.
() and "": These are parentheses and double quotes, respectively, which are used in Python syntax to indicate function arguments and string literals.

When this program is run, it will display the message “Hello World!” on the screen.

Note that Python is an interpreted language, which means that the code is executed directly without the need for a separate compilation step. The print() function is used to display output on the screen, and the string "Hello World!" is passed as an argument to this function to specify the message that should be displayed.

Key features:

Easy-to-read syntax
Extensive standard library
Large ecosystem of third-party libraries and frameworks (e.g., Django, Flask, NumPy)

3.2 JavaScript

JavaScript is a high-level, interpreted, and multi-paradigm programming language that is primarily used for client-side web development. It enables dynamic interactions between users and websites, making web pages more interactive and responsive. JavaScript has also gained popularity for server-side development through the Node.js runtime environment.

Example: HelloWorld.js

console.log("Hello World!");

console.log(): This is a built-in JavaScript function that is used to output text to the console, which is often used for debugging purposes.
"Hello World!": This is the message that will be output to the console. It is enclosed in double quotes to indicate that it is a string.
() and "": These are parentheses and double quotes, respectively, which are used in JavaScript syntax to indicate function arguments and string literals.

When this program is run, it will output the message “Hello World!” to the console.

Note that JavaScript is a scripting language that is typically run in a web browser. The console.log() function is used to output text to the browser console, which can be used to debug JavaScript code. In this case, the string "Hello World!" is passed as an argument to the console.log() function to specify the message that should be output to the console.

Key features:

Dynamically-typed language
Event-driven and asynchronous programming
Wide range of libraries and frameworks (e.g., React, Angular, Vue.js)

3.3 Java

Java is a high-level, compiled, and object-oriented programming language designed for platform independence. It is commonly used for web development, desktop applications, and Android app development. Java is known for its “write once, run anywhere” (WORA) philosophy, which enables developers to create code that runs on any platform supporting the Java Runtime Environment (JRE).

Example: HelloWorld.java

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

public class HelloWorld { }: This is a Java class definition, which defines a new class called HelloWorld. The public keyword indicates that the class can be accessed from outside the current package.
public static void main(String[] args) { }: This is the main method of the program, which is the entry point for execution. The public and static keywords indicate that the method can be accessed from outside the class, and can be called without creating an instance of the class. The void keyword indicates that the method does not return a value. The String[] args parameter is an array of strings that can be passed as command line arguments to the program.
System.out.println("Hello World!");: This line uses the println() method of the System.out object to output the message “Hello World!” to the console.

When this program is compiled and run, it will display the message “Hello World!” on the console.

Note that Java is a compiled language, which means that the code must be compiled into bytecode before it can be run. The public class definition is used to define a new class, and the public static void main() method is used to define the entry point for the program. The System.out.println() statement is used to output text to the console, and the string "Hello World!" is passed as an argument to this method to specify the message that should be output.

Key features:

Platform-independent
Strongly-typed language
Robust ecosystem (e.g., Spring, Hibernate, JavaFX)

3.4 C++

C++ is a high-level, compiled, general-purpose programming language that extends the C programming language with object-oriented features. It is widely used for system programming, game development, and high-performance applications. C++ offers a balance between performance and abstraction, making it a popular choice for complex projects.

Example: HelloWorld.cpp

#include <iostream>

int main() {
    std::cout << "Hello World!" << std::endl;
    return 0;
}

#include <iostream>: This line includes the standard input/output stream library, which provides access to functions like cout.
int main() { }: This is the main function where the program begins execution. int indicates that the function returns an integer. The empty parentheses indicate that the function takes no arguments.
std::cout << "Hello World!" << std::endl;: This line uses the << operator to output the message “Hello World!” to the console using the cout object. The std::endl statement is used to add a new line after the message is printed.
return 0;: This line exits the program and returns 0 to the operating system. By convention, a return value of 0 indicates successful execution of the program.

When this program is compiled and run, it will display the message “Hello World!” on the console.

Note that the #include statement is used to import external libraries in C++. In this case, we use the iostream library to access the cout object, which is used to output text to the console. The << operator is used to output the message “Hello World!” to the console, and the std::endl statement is used to add a new line after the message is printed. Finally, the return statement is used to exit the program and return a value to the operating system.

Key features:

Object-oriented programming support
Low-level memory manipulation
Rich standard library (e.g., Standard Template Library)

3.5 C#

C# (pronounced “C-sharp”) is a high-level, compiled, object-oriented programming language developed by Microsoft. It is primarily used for developing Windows applications and games using the .NET framework. C# offers features like garbage collection, type safety, and modern language constructs, making it a powerful language for a variety of applications.

Example: HelloWorld.cs

using System;

class HelloWorld {
    static void Main(string[] args) {
        Console.WriteLine("Hello World!");
    }
}

using System;: This line specifies that the program is using the System namespace, which contains the Console class.
class HelloWorld { }: This is a C# class definition, which defines a new class called HelloWorld.
static void Main(string[] args) { }: This is the main method of the program, which is the entry point for execution. The static keyword indicates that the method can be called without creating an instance of the class. The void keyword indicates that the method does not return a value. The string[] args parameter is an array of strings that can be passed as command line arguments to the program.
Console.WriteLine("Hello World!");: This line uses the WriteLine() method of the Console class to output the message “Hello World!” to the console.

When this program is compiled and run, it will display the message “Hello World!” on the console.

Note that C# is a compiled language, which means that the code must be compiled into bytecode before it can be run. The using statement is used to import the System namespace, which contains classes and methods for input and output operations. The class definition is used to define a new class, and the static void Main() method is used to define the entry point for the program. The Console.WriteLine() statement is used to output text to the console, and the string "Hello World!" is passed as an argument to this method to specify the message that should be output.

Key features:

Integrated with the .NET framework
Language Integrated Query (LINQ) support
Modern language features (e.g., async/await, pattern matching)

4. Conclusion

In this article, we provided an in-depth introduction to computer programming languages, covering their history, classification, and popular examples. Understanding the characteristics and differences between various programming languages can help developers make informed decisions when choosing the right language for their projects. As the world of programming continues to evolve, it is essential for developers to stay up-to-date with the latest languages, paradigms, and tools in order to create efficient and effective software solutions.

Learning CS from the Ground Up（4）

Understanding Computer Ⅳ:

Introduction to Computer Programming Languages

Table of Contents

1. History of Programming Languages

2. Classification of Programming Languages

2.1 High-Level vs Low-Level

2.2 Imperative vs Declarative

2.3 Compiled vs Interpreted

3. Popular Programming Languages

3.1 Python

3.2 JavaScript

3.3 Java

3.4 C++

3.5 C#

4. Conclusion