我不懂基本的C函数示例。请帮忙 [英] I don't understand basic C function example. PLEASE HELP

问题描述

int factorial(int x)
{
 int i;
 for(i=1; i < x; i++)
   x *= i;
 return x;
}

他们举了一个例子：

they gave an example of:

int a=5, b;
b = factorial(a);

并说：在这个短程序结束时，变量b将包含120，因为将使用参数5调用阶乘函数并返回120.



有人可以解释b是多少是120吗？

你能帮我看一下代码吗？

factorial（a）是什么意思？

将a的值替换为 x * =我？



我尝试过：



没什么，我只是在读一本关于它的书，我不明白。

and said: "At the end of this short program, the variable b will contain 120, since the factorial function will be called with the argument of 5 and will return 120."

Can some one explain how b is 120?
Can you also help me read the code?
What do they mean by " factorial(a) " ?
Did the substitute the value of a into " x *= i " ?

What I have tried:

Nothing, i was just reading a book about it and i don't understand.

推荐答案

你真的不能指望从技术论坛学习编程。你需要找一本更好的书，并尝试一些在线教程。



话虽如此，你提供的例子将无效。

You really cannot expect to learn programming from a technical forum. You need to find a better book, and try some online tutorials.

Having said that, the example you give will not work.

int factorial(int x)
{
 int i;
 for(i=1, i < x, i++) // set i to the value 1, while i is less than x
   x *= i;            // multiply x by the value of i [1 .. x-1]
                      // add 1 to i and repeat.

 return x;            // return the calculated value of x
// so if x starts at 5
// it becomes x * 1 ... 5   ... i starts at 1, x starts at 5
//            x * 2 ... 10  ... i is now 2 so the loop will have another 7
//                              iterations to perform
//            x * 3 ... 30  ... but i is now 3 so it will have another 26
//            x * 4 ... 120 ... i is now 4 and x is 120, so the loop will never terminate
}

阶乘函数只是一个数学特征。

The factorial function is just a mathematical feature.

Factorial是一个操作系统，您可以将所有值乘以一个限制，并在数学中用一个感叹号表示：3！，或6！或n！

A Factorial is an opertaion where you multiply all the values up to a limit, and in maths is expressed by an exlamation mark: 3!, or 6!, or n!

1!                          == 1
2! == 1 * 2                 == 2
3! == 1 * 2 * 3             == 6
4! == 1 * 2 * 3 * 4         == 24
5! == 1 * 2 * 3 * 4 * 5     == 120
6! == 1 * 2 * 3 * 4 * 5 * 6 == 720
...

你的代码中有一个函数，它传递一个数字（在一个名为<的变量中） code> x ）并返回该数字的因子，通过使用一个简单的循环来进行乘法。 （好吧，你会，如果那会编译 - for 循环使用分号，而不是逗号 - 如果它能正常工作 - 它不会：算法错误地实现了）



因此，当您修复 factorial 函数时，您可以在其中使用它的名称来调用它代码：

What you have in your code is a function which is passed a number (in a variable called x) and which returns the Factorial of that number, by using a simple loop to do the multiplication. (Well, you would, if that would compile - for loops use semicolons, not commas - and if it would work correctly if it did - which it won't: the algorithm is wrongly implemented)

So when you fix the factorial function you can call it by using it's name in your code:

b = factorial(a);

这会导致代码分支到阶乘函数，复制值在 a 进入 x 时到达那里，然后返回原始代码并将值放入阶乘返回（通过 return 语句）到变量 b



这就像你经常发布的文本列表一样，以节省你每次输入它们：你把它们放在记事本中，当你想发布一个时，你从记事本中复制它并粘贴到你的浏览器中。每个文本片段都是一个函数，copy'n'paste正在调用它进入你的帖子。有意义吗？

and that causes your code to "branch off" to the factorial function, copying the value in a into x when it gets there, then "comes back" to the original code and puts the value that factorial returned (via the return statement) into the variable b

It's like having a list of bits of text you post often to save you typing them out each time: you keep them in Notepad and when you want to post one, you copy it from Notepad and paste it into your browser. Each text fragment is a function and copy'n'paste is "calling" it into your post. Make sense?

请参阅 Factorial - Wikipedia [ ^ ]。



函数 int factorial（int x）是上述Wikipedia链接中描述的算法的C实现。



x * = i 与相同x = x * i 。



该示例声明了两个 int 变量并调用该函数执行计算其中值 a 作为参数传递，函数返回的结果存储在 b 中。

See Factorial - Wikipedia[^].

The function int factorial(int x) is a C implementation of the algorithm described in the above Wikipedia link.

x *= i is the same as x = x * i.

The example declares two int variables and calls the function to perform the calculation where the value a is passed as parameter and the result returned by the function is stored in b.

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