C編程語言允許使用一個循環內嵌套的另一個循環。下麵的內容展示幾個例子來說明這個概念。

語法

在C語言中嵌套for語句循環的語法如下：

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

在C編程語言中嵌套while循環聲明的語法如下：

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

在C編程語言嵌套do...while循環語句的語法如下：

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

}while( condition );

在循環嵌套最後需要說明的是，可以把任何類型的循環的任何其他類型的循環內。例如，對於環可以是一個while循環，或反之亦然內部。

例子：

下麵的程序使用嵌套for循環從2至100找出素數：

#include <stdio.h>
 
int main ()
{
   /* local variable definition */
   int i, j;
   
   for(i=2; i<100; i++) {
      for(j=2; j <= (i/j); j++)
        if(!(i%j)) break; // if factor found, not prime
      if(j > (i/j)) printf("%d is prime
", i);
   }
 
   return 0;
}

當上述代碼被編譯和執行時，它產生了以下結果：

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