02、ArkTS语法练习

```
// 变量声明

let hi: string = "hello word";
hi = "你好";

//常量声明
const hello: string = "world"; // 只能被赋值一次

const str: int =0;

// 类型推断
let hi1: string = "sdsd";
let hi2 = "nihao";
let age = 0;

// number类型
let n1 = 3.14;
let n2 = 3.2324234;
let n3 = .7;
let n4 = 1e2;

// 大整型
let bigIntger: BigInt = BigInt("2342342342342342342423423");
console.log(bigIntger.toString());

boolean类型
let isDone: boolean = false;
let isShow = false;
let isTop: boolean = true;

// string类型
let s1 = 'sdfgds';
let s2 = "sdsf";
let a = "sdsd";
let s3 = `sdgdsfg is ${ a }`;

//array 类型
let names: string[ ] = [ "zhangsan", "lisi", "wangwu" ];
let ages: int[ ] = [ 12, 234, 34, 5 ];

//enum类型
enum ColorSet { Red, Green, Blue };
let c: ColorSet = ColorSet.Red;

enum colorSet {
    Red = 0x00,
    Blue = 0xFF 
};
let f: colorSet = colorSet.Red;

// Union类型
class Cat { sleep () {}; eat () {}; }
class Dog { draw () {}; eat () {}; }
class Fash { draw () {}; falsh () {}; }

type Animal = Cat | Dog | Fash ;
let animal: Animal = new Cat ();
animal.eat();

function foo(animal: Animal) {
    if (animal instanceof Dog) {
        animal.draw();
    }
}

// 匿名类型
type Matrix = number[][];
type Handler = (r: string, n: number) => string;
type predicate<T> = (x: T) => boolean;
type NullableObject = object | null;

// 运算符
let isShow: boolean = false;
isShow = 9 === 8; // false
isShow = 9 === 9; // true
isShow = '9' === 9; // false

isShow =  '9' == 9;// true

// 语句
let s1 = "hello";
if (s1) {
    console.log(s1);
}

if(s1.length != 0) {
    console.log(s1);
}

let index: int = 9;
switch(index) {
    case 0 : ... break;
    case 1:  ... break;
    default : ...
}
```

```
// 表达式
let message = Math.random() > 0.5 ? "valid" : "Failed";
```

```
// For语句
let index =0;
for(let i = 0; i < 10; i++) {
    index +=1;
}
```

```
// For-of语句
for (let str of 'a string number') {
    console.log(str);
}
````

```
// while 语句
let index = 0;
while ( index < 10) {
    index ++;
    console.log(index);
}
```

```
// do-while 语句
let index = 0;
do {
    index ++;
    console.log( index );
} while ( index < 10 )
```

```
// break 语句
let index = 0;
while (true) {
    index ++;
    if ( index == 10) {
        break;
    }
}

// 如果 break 语句后带有标识符，则将控制流转移到该标识符所包含的语句块之外
index = 0;
label: while (true) {
    index +=  1;
    if ( index == 10) {
        break label;
    }
}
```

```
// continue语句 continue continue  continue
let index = 0;
for (let i = 0; i < 100; i ++) {
    if (i % 3 == 0) {
        continue;
    }
    console.log(i.toString());
}
```