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410 lines
10 KiB
Markdown
[#]: subject: "How different programming languages do the same thing"
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[#]: via: "https://opensource.com/article/21/4/compare-programming-languages"
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[#]: author: "Jim Hall https://opensource.com/users/jim-hall"
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[#]: collector: "lujun9972"
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[#]: translator: "VeryZZJ"
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[#]: reviewer: "wxy"
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[#]: publisher: "wxy"
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[#]: url: "https://linux.cn/article-14687-1.html"
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不同编程语言是如何完成同一件事
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======
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> 通过一个简单的小游戏比较 13 种编程语言。
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当我开始学习一种新的编程语言时，会把重点放在定义变量、书写声明以及计算表达式，一旦对这些概念有一个大致的了解，通常就能够自己弄清剩下的部分。大多数编程语言都具有相似性，所以如果你掌握了一种编程语言，学习下一种语言的重点就是弄清楚独有的概念以及区分不同。
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我喜欢写一些测试程序来帮助练习新的编程语言。其中我经常写的是一个叫做“猜数字”的小游戏，计算机选出 1 到 100 里的任一数字，然后我来猜。程序循环进行，直到猜出正确数字。通过伪代码可以看出，这是个非常简单的程序：
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* 计算机在 1 到 100 之间选出一个随机数字
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* 循环进行直到猜出该随机数字
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+ 计算机读取我的猜测
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+ 告诉我我的猜测过高还是过低
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我们发表了一些文章，用不同的语言写这个程序。这是一个比较不同语言做同样事情的有趣机会。大多数编程语言具有相似性，所以当你在学习下一种新的编程语言时，主要是学习它的独特之处。
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C 语言由 Dennis Ritchie 于 1972 年在贝尔实验室创建，是一种早期的通用编程语言。C 语言非常受欢迎，并迅速成为 Unix 系统上的标准编程语言。正是因为它的流行，许多其他编程语言也采用了类似的编程语法。这就是为什么如果你已经知道如何使用 C 语言编程，学习 C++、Rust、Java、Groovy、JavaScript、awk 或 Lua 会更容易。
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接下来我们看看这些不同的编程语言是如何实现 “猜数字” 游戏的主要步骤。我将把重点放在基本元素的相似或不同，跳过一些外围代码，如分配临时变量。
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### 计算机在 1 到 100 之间选出一个随机数字
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你可以看到这里有许多相似之处。大多数编程语言使用类似 `rand()` 的函数，你可以设定一个范围来生成随机数。而其他一些语言使用一个特殊的函数来设定范围生成随机数。
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C：
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```
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// Using the Linux `getrandom` system call
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getrandom(&randval, sizeof(int), GRND_NONBLOCK);
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number = randval % maxval + 1;
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// Using the standard C library
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number = rand() % 100 + 1;
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```
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C++：
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```
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int number = rand() % 100+1;
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```
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Rust：
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```
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let random = rng.gen_range(1..101);
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```
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Java：
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```
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private static final int NUMBER = r.nextInt(100) + 1;
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```
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Groovy：
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```
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int randomNumber = (new Random()).nextInt(100) + 1
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```
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JavaScript：
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```
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const randomNumber = Math.floor(Math.random() * 100) + 1
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```
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awk：
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```
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randomNumber = int(rand() * 100) + 1
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```
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Lua：
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```
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number = math.random(1,100)
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```
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### 循环进行直到我猜出该随机数字
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循环通常是用控制流程来实现的，如 `while` 或 `do-while`。JavaScript 中的实现没有使用循环，而是 “实时 ”更新 HTML 页面，直到用户猜出正确的数字。Awk 虽然支持循环，但是通过循环读取输入信息是没有意义的，因为 Awk 是基于数据管道的，所以它从文件而不是直接从用户读取输入信息。
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C：
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```
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do {
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…
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} while (guess != number);
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```
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C++：
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```
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do {
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…
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} while ( number != guess );
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```
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Rust：
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```
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for line in std::io::stdin().lock().lines() {
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…
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break;
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}
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```
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Java：
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```
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while ( guess != NUMBER ) {
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…
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}
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```
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Groovy：
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```
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while ( … ) {
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…
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break;
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}
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```
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Lua：
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```
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while ( player.guess ~= number ) do
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…
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end
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```
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### 计算机读取我的猜测
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不同编程语言对输入的处理方式不同。例如，JavaScript 直接从 HTML 表单中读取数值，而 Awk 则从数据管道中读取数据。
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C：
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```
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scanf("%d", &guess);
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```
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C++：
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```
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cin >> guess;
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```
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Rust：
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```
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let parsed = line.ok().as_deref().map(str::parse::<i64>);
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if let Some(Ok(guess)) = parsed {
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…
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}
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```
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Java：
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```
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guess = player.nextInt();
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```
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Groovy：
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```
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response = reader.readLine()
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int guess = response as Integer
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```
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JavaScript：
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```
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let myGuess = guess.value
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```
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Awk：
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```
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guess = int($0)
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```
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Lua：
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```
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player.answer = io.read()
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player.guess = tonumber(player.answer)
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```
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### 告诉我猜测过高还是过低
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在这些类 C 语言中，通常是通过 `if` 语句进行比较的。每种编程语言打印输出的方式有一些变化，但打印语句在每个样本中都是可识别的。
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C：
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```
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if (guess < number) {
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puts("Too low");
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}
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else if (guess > number) {
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puts("Too high");
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}
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…
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puts("That's right!");
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```
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C++：
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```
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if ( guess > number) { cout << "Too high.\n" << endl; }
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else if ( guess < number ) { cout << "Too low.\n" << endl; }
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else {
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cout << "That's right!\n" << endl;
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exit(0);
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}
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```
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Rust：
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```
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_ if guess < random => println!("Too low"),
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_ if guess > random => println!("Too high"),
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_ => {
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println!("That's right");
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break;
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}
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```
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Java：
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```
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if ( guess > NUMBER ) {
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System.out.println("Too high");
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} else if ( guess < NUMBER ) {
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System.out.println("Too low");
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} else {
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System.out.println("That's right!");
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System.exit(0);
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}
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```
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Groovy：
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```
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if (guess < randomNumber)
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print 'too low, try again: '
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else if (guess > randomNumber)
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print 'too high, try again: '
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else {
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println "that's right"
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break
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}
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```
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JavaScript：
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```
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if (myGuess === randomNumber) {
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feedback.textContent = "You got it right!"
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} else if (myGuess > randomNumber) {
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feedback.textContent = "Your guess was " + myGuess + ". That's too high. Try Again!"
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} else if (myGuess < randomNumber) {
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feedback.textContent = "Your guess was " + myGuess + ". That's too low. Try Again!"
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}
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```
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Awk：
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```
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if (guess < randomNumber) {
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printf "too low, try again:"
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} else if (guess > randomNumber) {
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printf "too high, try again:"
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} else {
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printf "that's right\n"
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exit
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}
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```
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Lua：
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```
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if ( player.guess > number ) then
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print("Too high")
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elseif ( player.guess < number) then
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print("Too low")
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else
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print("That's right!")
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os.exit()
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end
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```
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### 非类 C 编程语言会怎么样呢？
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非类 C 编程语言会有很大的不同，需要学习特定的语法来完成每一步。Racket 源于 Lisp 和 Scheme，所以它使用 Lisp 的前缀符和大量括号。Python 使用空格而不是括号来表示循环之类的块。Elixir 是一种函数式编程语言，有自己的语法。Bash 是基于 Unix 系统中的 Bourne shell，它本身借鉴了 Algol68，并支持额外的速记符，如 `&&` 作为 `and` 的变体。Fortran 是在使用打孔卡片输入代码的时期创建的，所以它依赖于一些重要列的 80 列布局。
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我将通过比较 `if` 语句，举例表现这些编程语言的不同。`if` 判断一个值是否小于或大于另一个值，并向用户打印适当信息。
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Racket：
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```
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(cond [(> number guess) (displayln "Too low") (inquire-user number)]
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[(< number guess) (displayln "Too high") (inquire-user number)]
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[else (displayln "Correct!")]))
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```
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Python：
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```
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if guess < random:
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print("Too low")
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elif guess > random:
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print("Too high")
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else:
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print("That's right!")
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```
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Elixir：
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```
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cond do
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guess < num ->
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IO.puts "Too low!"
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guess_loop(num)
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guess > num ->
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IO.puts "Too high!"
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guess_loop(num)
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true ->
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IO.puts "That's right!"
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end
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```
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Bash：
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```
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[ "0$guess" -lt $number ] && echo "Too low"
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[ "0$guess" -gt $number ] && echo "Too high"
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```
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Fortran：
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```
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IF (GUESS.LT.NUMBER) THEN
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PRINT *, 'TOO LOW'
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ELSE IF (GUESS.GT.NUMBER) THEN
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PRINT *, 'TOO HIGH'
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ENDIF
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```
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### 更多
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当你在学习一种新的编程语言时 “猜数字” 游戏是一个很友好的入门程序，通过一种简单的方式练习了几个常见的编程概念。通过不同编程语言实现这个简单游戏，你可以理解一些核心概念和每种语言的细节。
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学习如何用 C 和类 C 语言编写 “猜数字” 游戏：
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* [C][2]， Jim Hall
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* [C++][3]， Seth Kenlon
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* [Rust][4]， Moshe Zadka
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* [Java][5]， Seth Kenlon
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* [Groovy][6]， Chris Hermansen
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* [JavaScript][7]， Mandy Kendall
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* [awk][8]， Chris Hermansen
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* [Lua][9]， Seth Kenlon
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其他语言：
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* [Racket][10]， Cristiano L. Fontana
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* [Python][11]， Moshe Zadka
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* [Elixir][12]， Moshe Zadka
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* [Bash][13]， Jim Hall
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* [Fortran][14]， Jim Hall
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/4/compare-programming-languages
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作者：[Jim Hall][a]
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选题：[lujun9972][b]
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译者：[VeryZZJ](https://github.com/VeryZZJ)
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校对：[wxy](https://github.com/wxy)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/jim-hall
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/code_development_programming.png?itok=M_QDcgz5 "Developing code."
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[2]: https://opensource.com/article/21/1/learn-c
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[3]: https://opensource.com/article/20/12/learn-c-game
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[4]: https://opensource.com/article/20/12/learn-rust
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[5]: https://opensource.com/article/20/12/learn-java
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[6]: https://opensource.com/article/20/12/groovy
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[7]: https://opensource.com/article/21/1/learn-javascript
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[8]: https://opensource.com/article/21/1/learn-awk
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[9]: https://opensource.com/article/20/12/lua-guess-number-game
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[10]: https://opensource.com/article/21/1/racket-guess-number
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[11]: https://opensource.com/article/20/12/learn-python
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[12]: https://opensource.com/article/20/12/elixir
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[13]: https://opensource.com/article/20/12/learn-bash
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[14]: https://opensource.com/article/21/1/fortran
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