C#巢狀迴圈

C# 允許在一個迴圈中使用另一個迴圈。下面使用幾個例子來說明這個概念。

語法

C# 中的巢狀for迴圈語句的語法如下：

for ( init; condition; increment )
{
   for ( init; condition; increment )
   {
      statement(s);
   }
   statement(s);
}

C# 中的巢狀while迴圈語句的語法如下：

while(condition)
{
   while(condition)
   {
      statement(s);
   }
   statement(s);
}

C# 中的巢狀do...while迴圈語句的語法如下：

do
{
   statement(s);
   do
   {
      statement(s);
   }while( condition );

}while( condition );

可以將任何型別的迴圈放在任何其他型別的迴圈中。例如，for迴圈可以在while迴圈內，反之亦然。

範例

以下程式使用巢狀for迴圈來查詢從2到100內的素數：

using System;
namespace Loops
{
   class Program
   {
      static void Main(string[] args)
      {
         /* local variable definition */
         int i, j;
         for (i = 2; i < 100; i++)
         {
            for (j = 2; j <= (i / j); j++)
            if ((i % j) == 0) break; // if factor found, not prime
            if (j > (i / j))
            Console.WriteLine("{0} is prime", i);
         }
         Console.ReadLine();
      }
   }
}

當編譯和執行上述程式碼時，會產生以下結果：

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime