【初见Dart】第四章:控制语句

1. if语句

1.1 概述

- if语句
- if..else if语句
- if..else i..else语句

1.2 代码示例

void main() {
  int score = 100;//完美
  if (score >= 90) {
    if (score == 100) {
      print("完美");
    } else {
      print("优秀");
    }
  } else if (score > 60) {
    print("良好");
  } else if (score == 60) {
    print("及格");
  } else
    print("不及格");
  //完美
}

2. for语句

2.1 概述

- for循环
- for..in循环

2.2 代码示例

void main() {
  var list = [1, 2, 3, 4, 5];
  for (var index = 0; index < list.length; index++) {
    print(list[index]);
  }

  print("---------");

  for (var item in list) {
    print(item);
  }
  /**
   *  输出:
   *  1
      2
      3
      4
      5
      ---------
      1
      2
      3
      4
      5
   */
}

3. while语句

3.1 概述

- while循环
- do...while循环

3.2 代码示例

void main() {
  int count = 0;
  while (count < 5) {
    print(count++);
  }

  print("----$count----");

  do {
    print(count--);
  } while (count > 0 && count < 5);
  /**
   * 输出:
   *  0
      1
      2
      3
      4
      ----5----
      5
      4
      3
      2
      1
   */
}

4. break和continue

4.1 概述

- 终止循环:break
- 跳出当前循环:continue

4.2 代码示例

void main() {
  var list = [1, 2, 3];
  for (var item in list) {
    if (item == 1) {
      //break;
      continue;
    }
    print(item);
  }
  /**
   * 输出:
   *  2
      3
   */
  print("-----");

  var list2 = [4, 5, 6];
  for (var item1 in list) {
    if (item1 == 2) {
      break;
    }

    for (var item2 in list2) {
      if (item2 == 5) {
        break;
      }
      print(item2);
    }
  }
  //4
}

5. switch和case

5.1 概述

- 比较类型: num , String ,编译期常量,对象,枚举
- 非空case必须有一个break
- default处理默认情况
- continue跳转标签

5.2 代码示例

void main() {
  String language = "Java";

  switch (language) {
    case "Dart":
      print("Dart is my favorite");
      break;
    case "Java":
      print("Java is my favorite");
      break;
    case "Python":
      print("Python is my favorite");
      break;
    default:
      print("None");
  } //Java is my favorite

  switch (language) {
    Test:
    case "Dart":
      print("Dart is my favorite"); //3.再打印
      break; //4.跳出
    case "Java":
      print("Java is my favorite"); //1.先打印
      continue Test; //2.跳到Test:
    //break;
    case "Python":
      print("Python is my favorite");
      break;
    default:
      print("None");
  }
  /**
   * 输出:
   *  Java is my favorite
      Dart is my favorite
   */
}