C++嵌套循环

循环可以嵌套在另一个循环内。C++允许至少256级嵌套。

语法

C++中嵌套for循环语句的语法如下：

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

C++中嵌套while循环语句的语法如下：

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

C++中嵌套do...while循环语句的语法如下：

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

} while( condition );

示例

下面的程序使用嵌套for循环来查找2到100之间的素数：

#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;
}

这将产生以下结果：

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