Objective-C 嵌套循环

Objective-C 编程语言支持在另一个循环中使用一个循环。下一节展示了几个例子来说明这个概念。

语法

嵌套循环 语句在 C 语言中的语法如下:

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

嵌套循环 语句在 Objective-C 语言中的语法如下:

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

Objective-C 语言中的 嵌套 do…while 循环 语句语法如下:

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

关于 循环嵌套 的最后一点是，您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 循环可以在 while 循环内，反之亦然。

实例

下面的程序使用嵌套的 for 循环来查找 2 到 100 之间的素数:

#import <Foundation/Foundation.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)) NSLog(@"%d is prime\n", i);
  }
  return 0;
}

结果如下:

2022-09-07 22:40:01.004 demo[1027] 2 is prime
2022-09-07 22:40:01.005 demo[1027] 3 is prime
2022-09-07 22:40:01.005 demo[1027] 5 is prime
2022-09-07 22:40:01.005 demo[1027] 7 is prime
2022-09-07 22:40:01.005 demo[1027] 11 is prime
2022-09-07 22:40:01.005 demo[1027] 13 is prime
2022-09-07 22:40:01.005 demo[1027] 17 is prime
2022-09-07 22:40:01.005 demo[1027] 19 is prime
2022-09-07 22:40:01.005 demo[1027] 23 is prime
2022-09-07 22:40:01.005 demo[1027] 29 is prime
2022-09-07 22:40:01.005 demo[1027] 31 is prime
2022-09-07 22:40:01.005 demo[1027] 37 is prime
2022-09-07 22:40:01.005 demo[1027] 41 is prime
2022-09-07 22:40:01.005 demo[1027] 43 is prime
2022-09-07 22:40:01.005 demo[1027] 47 is prime
2022-09-07 22:40:01.005 demo[1027] 53 is prime
2022-09-07 22:40:01.005 demo[1027] 59 is prime
2022-09-07 22:40:01.005 demo[1027] 61 is prime
2022-09-07 22:40:01.005 demo[1027] 67 is prime
2022-09-07 22:40:01.005 demo[1027] 71 is prime
2022-09-07 22:40:01.005 demo[1027] 73 is prime
2022-09-07 22:40:01.005 demo[1027] 79 is prime
2022-09-07 22:40:01.005 demo[1027] 83 is prime
2022-09-07 22:40:01.005 demo[1027] 89 is prime
2022-09-07 22:40:01.005 demo[1027] 97 is prime