Flutter(三) Dart语言基础-运算符

本文主要介绍运算符相关操作

算术运算符

• 加减乘除: + , - , * , / , % , ~/
• 递增递减: var++ , var-- , ++var , --var

  double a = 10.0;
  double b = 2.0;

  print(a + b);
  //12.0
  print(a - b);
  //8.0
  print(a * b);
  //20.0
  print(a / b);
  //5.0
  print(a % b);
  //0.0
  print(a ~/ b);
  //5

  print(a++);
  //10.0  a++ 是a使用以后a+1 表达式之后a此时为11.0
  print(++a);
  //12.0  ++a 是a使用之前a+1 a从 11.0+1 = 12.0
  print(a--);
  //12.0 a-- 是a使用之后a-1 表达式之后a 此时为11.0
  print(--a);
  //10.0 --a 是a使用之前a-1 a 从 11.0-1 = 10.0

关系运算符

• 运算符: == , != , > , < , >= , <=
• 判断内容是否相同; ==

  int a = 5;
  int b = 3;
  print(a == b);
  //false
  print(a != b);
  //true
  print(a > b);
  //true
  print(a < b);
  //false
  print(a >= b);
  //true
  print(a <= b);
  //false

  String str1 = "123";
  String str2 = "123";
  String str3 = "321";
  print(str1 == str2);
  //true
  print(str1 == str3);
  //false

逻辑运算符

• 运算符: ! , && , ||
• 针对布尔型运算

  bool isTrue = true;
  print(!isTrue);
  //false

  bool isFalse = false;
  print(isTrue && isFalse);
  //false  同时为true 才为true
  print(isTrue || isFalse);
  //true  两个有一个为true 就为true

  String str = "";
  print(!str.isEmpty);
  //false

赋值运算符

• 基础运算符: = , ??=
• 复合运算符: += , -= , *= , /= , %= , ~/=

  int a = 10;
  int b = 5;
  int c;
  b ??= 10;
  print(b);
  //5  b有值取b的值
  c ??= 10;
  print(c);
  //10 c没有值,赋值10
  a += b; //相当于a = a + b;
  print(a);
  //15
  a -= b; //相当于a = a - b;
  print(a);
  //10;
  a *= b; //相当于a = a * b;
  print(a);
  //50
  // a /= b;//a为int 使用/=是double,所以报错
  a %= b; //相当于a = a % b;
  print(a);
  //0
  a ~/= b; //相当于a = a ~/ b;
  print(a);
  //0

条件表达式

• 三目运算符: condition ? expr1 : expr2
• ??运算符: expr1 ?? expr2

  int gendar = 1;
  String str = gendar == 1 ? "Male" : "Female";
  print(str);
  //Male

  String str1 = "Dart";
  String str2 = "Java";
  String str3;
  String str4 = str2 ?? str1;//str2有值取str2,无值取str1
  print(str4);
  //Java  
  String str5 = str3 ?? str1;//str3有值取str3,无值取str1
  print(str5);
  //Dart