递归循环（C＃） [英] Recursive loop (C#)

问题描述

有人可以向我解释吗？我写了一个函数来计算这样一个数字在C＃中的阶乘：

Can someone please explain it to me? I wrote a function to calculate the factorial of a number like this in C#:

public int factorial(int input)
{
    if (input == 0 || input == 1)
        return 1;
else
{
    int temp = 1;
    for (int i = 1; i <= input; i++)
        temp = temp * i;
    return temp;
    }
}

但我发现了一些C ++代码真的知道任何C ++ btw）使用递归循环找到一个阶乘：

But I found some C++ code (I don't really know any C++ btw) which finds a factorial using a recursive loop:

int factorial(int number) {
 int temp;
 if(number <= 1) return 1;
 temp = number * factorial(number - 1);
 return temp;
}

有人可以向我解释它是如何工作的？感谢。

Can someone explain to me how it works? Thanks.

推荐答案

在语法上，C ++代码与用C＃编写的代码完全相同。不要让语言差异抓住你！它实际上看起来像C给我，假定变量被声明在函数的顶部;这在C ++或C＃中不是绝对必要的。我喜欢在第一次使用它们时声明变量，将声明和初始化结合在一个语句中，但这只是一种不改变代码功能的样式偏好。

Syntactically, the C++ code is identical to the same code written in C#. Don't let the language discrepancy catch you off guard! It actually looks like C to me, given that the variable is declared at the top of the function; that's not strictly necessary in either C++ or C#. I prefer to declare variables the first time I use them, combining the declaration and initialization in one single statement, but that's merely a stylistic preference that doesn't change the function of the code.

我将尝试通过向代码段的每一行添加注释来解释这一点：

I'll try to explain this by adding comments to each line of the code snippet:

// Declare a function named "Factorial" that accepts a single integer parameter,
// and returns an integer value.
int Factorial(int number)
{
    // Declare a temporary variable of type integer
    int temp;

    // This is a guard clause that returns from the function immediately
    // if the value of the argument is less than or equal to 1.
    // In that case, it simply returns a value of 1.
    // (This is important to prevent the function from recursively calling itself
    // forever, producing an infinite loop!)
    if(number <= 1) return 1;

    // Set the value of the temp variable equal to the value of the argument
    // multiplied by a recursive call to the Factorial function
    temp = number * Factorial(number - 1);

    // Return the value of the temporary variable
   return temp;
}

递归调用仅仅意味着该函数从同一个函数内调用自身。这是因为n的阶乘相当于以下语句：

Recursive calls simply mean that the function calls itself from within the same function. This works because the factorial of n is equivalent to the following statement:

n! = n * (n-1)! 

一个伟大的方式来了解代码的工作原理是将它添加到测试项目，然后使用调试器单步执行代码。 Visual Studio在C＃应用程序中有非常丰富的支持。您可以观察函数如何递归调用自身，观察每行执行顺序，甚至看到变量的值随着对它们执行操作而改变。

One great way to understand how code works is to add it to a test project, then single-step through the code using the debugger. Visual Studio has very rich support for this in C# applications. You can watch how the function recursively calls itself, watching each line execute in sequence, and even seeing the values of the variables change as operations are performed on them.

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