【初见Dart】第四章:控制语句

第四章:控制语句

• ​​1. if语句​​

• ​​1.1 概述​​
• ​​1.2 代码示例​​

• ​​2. for语句​​

• ​​2.1 概述​​
• ​​2.2 代码示例​​

• ​​3. while语句​​

• ​​3.1 概述​​
• ​​3.2 代码示例​​

• ​​4. break和continue​​

• ​​4.1 概述​​
• ​​4.2 代码示例​​

• ​​5. switch和case​​

• ​​5.1 概述​​
• ​​5.2 代码示例​​

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
*/
}