Objective-C 中的嵌套循环

Objective-C 编程语言允许在一个循环内使用另一个循环。 以下部分显示了几个示例来说明这个概念。

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);
}

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);
}

在 Objective-C 编程语言中，嵌套的 do...while 循环语句的语法如下 −

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内。 例如，for 循环可以在 while 循环内，反之亦然。

示例

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;
}

当上面的代码被编译和执行时，会产生如下结果 −

2013-09-07 22:40:01.004 demo[1027] 2 is prime
2013-09-07 22:40:01.005 demo[1027] 3 is prime
2013-09-07 22:40:01.005 demo[1027] 5 is prime
2013-09-07 22:40:01.005 demo[1027] 7 is prime
2013-09-07 22:40:01.005 demo[1027] 11 is prime
2013-09-07 22:40:01.005 demo[1027] 13 is prime
2013-09-07 22:40:01.005 demo[1027] 17 is prime
2013-09-07 22:40:01.005 demo[1027] 19 is prime
2013-09-07 22:40:01.005 demo[1027] 23 is prime
2013-09-07 22:40:01.005 demo[1027] 29 is prime
2013-09-07 22:40:01.005 demo[1027] 31 is prime
2013-09-07 22:40:01.005 demo[1027] 37 is prime
2013-09-07 22:40:01.005 demo[1027] 41 is prime
2013-09-07 22:40:01.005 demo[1027] 43 is prime
2013-09-07 22:40:01.005 demo[1027] 47 is prime
2013-09-07 22:40:01.005 demo[1027] 53 is prime
2013-09-07 22:40:01.005 demo[1027] 59 is prime
2013-09-07 22:40:01.005 demo[1027] 61 is prime
2013-09-07 22:40:01.005 demo[1027] 67 is prime
2013-09-07 22:40:01.005 demo[1027] 71 is prime
2013-09-07 22:40:01.005 demo[1027] 73 is prime
2013-09-07 22:40:01.005 demo[1027] 79 is prime
2013-09-07 22:40:01.005 demo[1027] 83 is prime
2013-09-07 22:40:01.005 demo[1027] 89 is prime
2013-09-07 22:40:01.005 demo[1027] 97 is prime

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