两个 for 循环的优缺点    for (i=0; i<N; i++)                      |     if (condition) {                                                 |     {    if (condition)                         |   for (i=0; i<N; i++)      DoSomething();                  |     DoSomething();    else                                        |      }      DoOtherthing();                  |     else }                                                 |     {                                                   |  for (i=0; i<N; i++)                                                    |     DoOtherthing();                                                   |     } 优点：程序简洁                       |                                                      | 优点：循环的效率高 缺点：多执行了 N-1 次逻辑    | 判断，并且打断了循环“流水 | 缺点：程序不简洁 线”作业，使得编译器不能对 | 循环进行优化处理，降低了效 | 率。      |