Dart学习笔记-控制语句

Posted 2022-12-07 追到梦的魔术师

一、if、else、else if

  int score = 43;
  
  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");
  

执行结果：不及格

二、for、forin

  var list = [1,2,3,4,5];
  for(var index = 0;index < list.length; index++)
    print(list[index]);
  
  
  for(var item in list)
    print(item);
  

执行结果：
1
2
3
4
5
1
2
3
4
5

三、while、do…while

  int count = 0;
  while(count < 5)
    print(count++);
  
  
  print("-----------$count-------------");
  
  do
    print(count--);
  while(count > 0 && count < 5);

执行结果：
0
1
2
3
4
-----------5-------------
5
4
3
2
1

四、break、continue

  var list1 = [1,2,3];
  for(var item in list1)
    if(item == 2)
      break;
    
    print(item);
  

执行结果：1

  var list1 = [1,2,3];
  for(var item in list1)
    if(item == 2)
      break;
    
    print(item);
  

执行结果：
1
3

组合使用，循环嵌套

  var list1 = [1,2,3];
  var list2 = [4,5,6];
  for(var item1 in list1)
    if(item1 == 2)
      break;
    
    for(var item2 in list2)
      if(item2 == 5)
        break;
      
      print(item2);
    
  

执行结果：4
注意：break只会跳出break所在最内层的循环

五、switch case

 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"); 
  
  

执行结果：Java is my favorite

特殊用法：语法——continue+标签
程序会直接跳转到标签标识的case位置继续执行

  String language = "Java";
  switch(language)
    Tag:
    case "Dart":
      print("Dart is my favorite");
      break;
    case "Java":
      print("Java is my favorite");
      continue Tag;

    case "Python":
      print("Python is my favorite");
      break;
    default:
      print("None"); 
  

执行结果：
Java is my favorite
Dart is my favorite

先执行case “Java”，打印：“Java is my favorite”，之后continue Tag，程序跳转到名字为Tag的标签位置，Tag标识在case "Dart"之前，程序便跳转到case "Dart"继续执行，打印：“art is my favorite”