Dart之常用数据类型(字符串、数值、布尔、集合、映射)

main() {
//  1、字符串的定义方式
//推导类型双引号定义
  var str1 = "hello1";
  //推导类型单引号定义
  var str2 = 'hello2';
  //指定类型单引号定义
  String str3 = 'hello3';
  //指定类型双引号定义
  String str4 = "hello4";
//多行文本
  String str5 = '''hello
world
 ''';
  print(str1); //hello1
  print(str2); //hello2
  print(str3); //hello3
  print(str4); //hello4
  print(str5);
  /**
   * hello
      world
   */
  
  
//  字符串拼接
  print("$str1 $str2"); //hello1 hello2
  print(str1 + str2); //hello1hello2
}

main() {
//  1、int
  int a = 123;
  print(a); //123
//2、double
  double b = 34.34;
  double c = 32;
  print(b); //34.34
  print(c); //32.0
  print("-------------------------");
//3、运算符
  var d = a + b;
  var e = a - b;
  var f = a * b;
  var g = a / b;
  var h = a % b;
  print(d); //157.34
  print(e); //88.66
  print(f); //4223.820000000001
  print(g); //3.581828771112405
  print(h); //19.97999999999999
}

main() {
  //1、bool
  bool flag = true;
  bool flag2 = false;
  print(flag); //true
  print(flag2); //false
//  2、条件判断语句
  int a = 1;
  int b = 2;
  if (a < b) {
    print("a<b"); //a<b
  } else {
    print("b<2");
  }
 
  print(a == b); //false
  String c = "aaffa";
  print(a == c); //false
}

main() {
//  1、第一种定义List的方式
  var l1 = ["张珊", 20, true];
  print(l1.length); //3
  print(l1); //[张珊, 20, true]
  print(l1[0]); //张珊
  print(l1.first); //张珊
  print(l1.last); //true
  print(l1.isEmpty); //false
  print(l1.join(":")); //张珊:20:true
  print("-------------------------");
 
//2、第二种定义List的方式
  var l2 = <String>["a", "b", "c"];
  print(l2); //[a, b, c]
  l2.length = 0;
  print(l2); //[]
  print("-------------------------");
//3、第三种定义list
  var l3 = [];
  l3.add("qw");
  l3.add("qe");
  print(l3); //[qw, qe]
  print("-------------------------");
//4、第四种方式,固定长度,无法增加数据、无法修改长度
  var l4 = List.filled(2, "1");
  print(l4); //[1, 1]
  l4.add("a"); //Cannot add to a fixed-length list
  l4.add("b");
  l4.add("c");
  print(l4);
  var l5 = List<int>.filled(2, 26);
  print(l5);
}

main() {
//  第一种定义 maps的方式
  var person = {"name": "zhangshan", 'age': 56};
  print(person); //{name: zhangshan, age: 56}
  print(person['age']); //56
  print(person["name"]); //zhangsan
  print("-------------------------");
//  第二种定义方式
  var per = new Map();
  per['name'] = "lisi";
  per['age'] = 23;
  print(per); //{name: lisi, age: 23}
}

main(){
  var flag=true;
  if(flag is String){
    print("String");
  }else if(flag is int){
    print("int");
  }else if(flag is bool){
    print("bool"); //bool
  }
}