Objective-C嵌套循环

Objective-C编程语言允许在另一个循环中使用一个循环。以下部分显示了几个例子来说明这个概念。

语法

Objective-C语言中嵌套for循环语句的语法如下 -

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

Objective-C编程语言中嵌套while循环语句的语法如下 -

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

Objective-C编程语言中嵌套do...while循环语句的语法如下 -

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

} while( condition );

循环嵌套可以将任何类型的循环放在任何其他类型的循环中。 例如，for循环可以放在while循环内，反之亦然。

例子
以下程序使用嵌套for循环来从2到100中查找素数 -

#import <Foundation/Foundation.h>

int main () {

   /* 局部变量定义 */
   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)) NSLog(@"%d is prime\n", i);
   }

   return 0;
}

执行上面示例代码，得到以下结果：

2018-11-14 07:14:35.503 main[60729] 2 is prime
2018-11-14 07:14:35.505 main[60729] 3 is prime
2018-11-14 07:14:35.505 main[60729] 5 is prime
2018-11-14 07:14:35.505 main[60729] 7 is prime
2018-11-14 07:14:35.505 main[60729] 11 is prime
2018-11-14 07:14:35.506 main[60729] 13 is prime
2018-11-14 07:14:35.506 main[60729] 17 is prime
2018-11-14 07:14:35.506 main[60729] 19 is prime
2018-11-14 07:14:35.506 main[60729] 23 is prime
2018-11-14 07:14:35.506 main[60729] 29 is prime
2018-11-14 07:14:35.506 main[60729] 31 is prime
2018-11-14 07:14:35.506 main[60729] 37 is prime
2018-11-14 07:14:35.506 main[60729] 41 is prime
2018-11-14 07:14:35.506 main[60729] 43 is prime
2018-11-14 07:14:35.506 main[60729] 47 is prime
2018-11-14 07:14:35.506 main[60729] 53 is prime
2018-11-14 07:14:35.506 main[60729] 59 is prime
2018-11-14 07:14:35.506 main[60729] 61 is prime
2018-11-14 07:14:35.506 main[60729] 67 is prime
2018-11-14 07:14:35.506 main[60729] 71 is prime
2018-11-14 07:14:35.506 main[60729] 73 is prime
2018-11-14 07:14:35.506 main[60729] 79 is prime
2018-11-14 07:14:35.506 main[60729] 83 is prime
2018-11-14 07:14:35.506 main[60729] 89 is prime
2018-11-14 07:14:35.506 main[60729] 97 is prime