C++巢狀迴圈

迴圈可以巢狀在另一個迴圈內。C++允許至少256級巢狀。

語法

C++中巢狀for迴圈語句的語法如下：

for ( init; condition; increment ) {
   for ( init; condition; increment ) {
      statement(s);
   }
   statement(s); // you can put more statements.
}

C++中巢狀while迴圈語句的語法如下：

while(condition) {
   while(condition) {
      statement(s);
   }
   statement(s); // you can put more statements.
}

C++中巢狀do...while迴圈語句的語法如下：

do {
   statement(s); // you can put more statements.
   do {
      statement(s);
   } while( condition );

} while( condition );

示例

下面的程式使用巢狀for迴圈來查詢2到100之間的素數：

#include <iostream>
using namespace std;
 
int main () {
   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)) cout << i << " is prime\n";
   }
   
   return 0;
}

這將產生以下結果：

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