第19节：Objective-C 嵌套循环


Objective-C语言的编程语言允许使用一个循环的另一循环内。下面的部分显示了几个例子来说明这个概念。

语法:

嵌套的for循环语句在C的语法如下：

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

 nested while loop 语句的语法在Objective-C编程语言的语句如下：

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

嵌套 nested do...while loop 语句语法在Objective-C编程语言的语句如下：

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

}while( condition );

循环嵌套最后需要说明的是，你可以把任何类型的循环内的任何其他类型的循环。例如，一个for循环，可以在while循环或反之亦然。

例如：

下面的程序使用嵌套的for循环找出2〜100中的素数

#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
", i);
   }
 
   return 0;
}

上面的代码编译和执行时，它会产生以下结果：

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

来源：https://www.yiibai.com/objective_c/objective_c_nested_loops.html


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