Question

我正在学习C＃并且无法理解这个循环。它显示

“循环8次” “循环9次” “循环9次”

但据我了解，它应该显示出来 “循环8次” “循环9次” “循环10次”

我尝试使用调试工具来帮助我查看，但实际上并不确定在哪里放置断点来帮助我。你能帮我解释一下它为什么是递归的以及它是如何工作的？

namespace LoopTest
{
    class Program
    {
        private static int WriteToConsole(int numberOfWrites)
        {
            for (int i = numberOfWrites; i < 10; i = WriteToConsole(i + 1))
            {
                Console.WriteLine("Looped {0} times.", i);
            }
            return numberOfWrites;
        }
        static void Main(string[] args)
        {
            WriteToConsole(8);
            Console.ReadKey();
        }
    }
}

Answer 1

这是因为你经常调用这个方法，所以对于第一个函数调用if将被迭代为8和9，而递归调用只有一次，所以对于9。

所以它就像那样

WriteToConsole(8)//, it's < 10 so it will print the call with 8 and call the same method with 9
 WriteToConsole(9)//, it's < 9 so it will print the call with 9 and **not** call the same method with 10 (as it's  not < 10) and return 9 as the result of the function
//Then it returns to the first call, with returned int 9 as i and it will print 9 again as the first call result

我将使用'＆lt; ='代替'＆lt;'

来解释一个示例

WriteToConsole(8) //1st level, prints 8, calls recursively 9
| WriteToConsole(9)//2nd level, prints 9, calls recursively 10
|| WriteToConsole(10)//3rd level, prints 10, calls recursively 11
||| WriteToConsole(11) //4th level, doesn't print anything (>10) and returns 11
|| Loop does not execute as returned i = 11 so > 10, returns 10 (because WriteToConsole(10) was initially called)
| WriteToConsole(10)//2nd level, prints 10, calls recursively 11
|| WriteToConsole(11) //3rd level, doesn't print anything (>10) and returns 11
| Loop does not execute as returned i = 11 so > 10, returns 10 (because WriteToConsole(9) was initially called)
WriteToConsole(9) //1st level, prints 9, calls recursively 10
| WriteToConsole(10) //2nd level, prints 10, calls recursively 11
|| WriteToConsole(11) //3rd level, doesn't print anything (>10) and returns 11
| Loop does not execute as returned i = 11 so > 10, returns 10 (because WriteToConsole(10) was initially called)
WriteToConsole(10) //1st level, prints 10, calls recursively 11
| WriteToConsole(11) //2nd level, doesn't print anything (>10) and returns 11
Loop does not execute as returned i = 11 so > 10, returns 8 (because WriteToConsole(10) was initially called)

为了说明，我已经添加了递归级别参数以及更多日志记录到您的代码中，您可以在我的dotnetfiddle（https://dotnetfiddle.net/het1w1）上看到，这是结果：

Looped 8 times. Recursion level 1
Looped 9 times. Recursion level 2
Looped 10 times. Recursion level 3
returned: 11
returned: 10
Looped 10 times. Recursion level 2
returned: 11
returned: 9
Looped 9 times. Recursion level 1
Looped 10 times. Recursion level 2
returned: 11
returned: 10
Looped 10 times. Recursion level 1
returned: 11
returned: 8

Answer 2

这是因为你只使用<（小于）你需要将其更改为<=（等于或小于），这将包括第10个：

namespace LoopTest
    {
        class Program
        {
            private static int WriteToConsole(int numberOfWrites)
            {
                for (int i = numberOfWrites; i <= 10; i = WriteToConsole(i + 1))
                {
                    Console.WriteLine("Looped {0} times.", i);
                }
                return numberOfWrites;
            }
            static void Main(string[] args)
            {
                WriteToConsole(8);
                Console.ReadKey();
            }
        }
    }

Answer 3

您需要将for循环更改为

number (int) | time_stamp (datetime2) | number2 (int) | time_stamp2 (datetime2)
--------------------------------------------------------
20           | '2017-08-01 01:00:00'  | null          | null
100          | '2017-08-01 01:00:00'  | null          | null

Answer 4

这只是因为你在for循环增量语句中使用了 WriteToConsole

请替换此行

for (int i = numberOfWrites; i <= 10; i = WriteToConsole(i + 1))

带

for (int i = numberOfWrites; i <= 10; i = i + 1)

这样你就可以轻松理解循环。

Answer 5

当您致电WriteToConsole(8);时，该方法内的for循环将：

设置i = 8
评估i＆lt; 10这是真的，所以执行循环内部的内容：Console.WriteLine("Looped 8 times.");
设置i：i = WriteToConsole(i + 1)的值，此行将再次调用（递归）WriteToConsole（9）;

使用numberOfWrites = 9：Console.WriteLine("Looped 9 times.");

但不要忘记第一种方法（WriteToConsole(8);）尚未完成。我们在设置i的值时离开了该方法。因此，如果您恢复i = 9的for循环：Console.WriteLine("Looped 9 times.");

我认为你错过了for循环中的控制流：https://www.tutorialspoint.com/csharp/csharp_for_loop.htm

解释这个递归循环

5 个答案: