C# - 巢狀迴圈

C# 允許在一個迴圈內使用另一個迴圈。以下部分顯示了一些示例來說明此概念。

語法

C# 中巢狀 for 迴圈語句的語法如下所示：

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

C# 中巢狀 while 迴圈語句的語法如下所示：

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

C# 中巢狀 do...while 迴圈語句的語法如下所示：

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

關於迴圈巢狀的最後一點是，您可以將任何型別的迴圈放在任何其他型別的迴圈內。例如，for 迴圈可以在 while 迴圈內，反之亦然。

示例

以下程式使用巢狀 for 迴圈查詢 2 到 100 之間的素數：

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();
      }
   }
} 

編譯並執行上述程式碼後，將產生以下結果：

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