Dart – 循环控制语句（Break 和 Continue）

Dart支持两种类型的循环控制语句：

1. 中断声明
2. 继续声明

中断声明：

此语句用于中断循环的控制流，即如果它在循环中使用，则无论何时遇到它都会终止循环。它会将控制流带出最近的循环。

句法：

break;

示例 1：在 while 循环中使用 break

void main()
{
    int count = 1;
  
    while (count <= 10) {
        print("Geek, you are inside loop $count");
        count++;
  
        if (count == 4) {
            break;
        }
    }
    print("Geek, you are out of while loop");
}

输出：

Geek, you are inside loop 1
Geek, you are inside loop 2
Geek, you are inside loop 3
Geek, you are out of while loop

解释：
最初计数值为 1，当它进入循环时，检查条件 1 <= 10 并且当它为真时，语句打印变量增加，然后检查条件， 2 == 4，这是false 。然后再次循环，直到遇到条件 4 == 4 并且流程退出循环，然后执行最后一个打印语句。

示例 2：在 do..while 循环中使用 break

void main()
{
    int count = 1;
  
    do {
        print("Geek, you are inside loop $count");
        count++;
  
        if (count == 5) {
            break;
        }
    } while (count <= 10);
    print("Geek, you are out of do..while loop");
}

输出：

Geek, you are inside loop 1
Geek, you are inside loop 2
Geek, you are inside loop 3
Geek, you are inside loop 4
Geek, you are out of do..while loop

示例 3：在 for 循环中使用 break

void main()
{
    for (int i = 1; i <= 10; ++i) {
        if (i == 2)
            break;
  
        print("Geek, you are inside loop $i");
    }
  
    print("Geek, you are out of loop");
}

输出：

Geek, you are inside loop 1
Geek, you are out of loop

继续声明：

中断用于结束控制流，而继续则用于继续控制流。当在循环中遇到 continue 语句时，它不会终止循环，而是将流程跳转到下一次迭代。

句法：

continue;

示例 1：在 while 循环中使用 continue

void main()
{
    int count = 0;
  
    while (count <= 10) {
        count++;
  
        if (count == 4) {
            print("Number 4 is skipped");
            continue;
        }
  
        print("Geek, you are inside loop $count");
    }
  
    print("Geek, you are out of while loop");
}

输出：

Geek, you are inside loop 1
Geek, you are inside loop 2
Geek, you are inside loop 3
Number 4 is skipped
Geek, you are inside loop 5
Geek, you are inside loop 6
Geek, you are inside loop 7
Geek, you are inside loop 8
Geek, you are inside loop 9
Geek, you are inside loop 10
Geek, you are inside loop 11
Geek, you are out of while loop

解释：
这里循环的控制流将变得顺畅，但是当计数值变为 4 时，if 条件变为真，并且由于 continue 和下一次迭代跳过数字 4 而跳过下面的语句。

示例 2：在 do..while 循环中使用 continue

void main()
{
    int count = 0;
  
    do {
        count++;
  
        if (count == 4) {
            print("Number 4 is skipped");
            continue;
        }
  
        print("Geek, you are inside loop $count");
    } while (count <= 10);
    print("Geek, you are out of while loop");
}

输出：

Geek, you are inside loop 1
Geek, you are inside loop 2
Geek, you are inside loop 3
Number 4 is skipped
Geek, you are inside loop 5
Geek, you are inside loop 6
Geek, you are inside loop 7
Geek, you are inside loop 8
Geek, you are inside loop 9
Geek, you are inside loop 10
Geek, you are inside loop 11
Geek, you are out of while loop

示例 3：在 for 循环中使用 continue

void main()
{
    for (int i = 1; i <= 10; ++i) {
  
        if (i == 2) {
            print("Geek, you are inside loop $i");
            continue;
        }
    }
  
    print("Geek, you are out of loop");
}

输出：

Geek, you are inside loop 2
Geek, you are out of loop