12. 循环结构-do while循环

1、do while循环

1）do wilie循环语法

2）习题1

Ⅰ 使用while循环

操作如下：

import java.util.Scanner;
public class Demo12 {
    	public static void main(String[] args) {
    		Scanner superman = new Scanner(System.in);
    		String name = "a";  // 这里给name一个初始条件
    		while (name.equals("q") == false){
    			System.out.print("请输入学员的姓名:");
    			name = superman.next();
    		}
	}
}

结果如下：

Ⅱ 使用do while循环

操作如下：

import java.util.Scanner;
public class Demo1 {
    	public static void main(String[] args) {
    		String name;
    		Scanner superman = new Scanner(System.in);
    		do{
    			System.out.print("请输入学员的姓名:");
    			name = superman.next();
    		}while (!(name.equals("q")));   // 为true，继续执行循环；否则跳出循环。
	}
}

结果如下：

2）习题2

具体需求如下：

代码如下：

import java.util.Scanner;
public class Demo3 {
    	public static void main(String[] args) {
    		Scanner superman = new Scanner(System.in);
    		System.out.println("请输入选择购买的商品编号:");
                System.out.println("         商品列表        ");
    		System.out.println("1.T恤\t2.网球鞋\t3.网球拍");
    		System.out.println("*********************************");
    		int num;
    	String str;
    	String str1;
    	System.out.print("是否想继续,请输入y/n:");
    	str = superman.next();
    	switch (str){
    	case "y":
    		System.out.println("-----------*____*-------------");
    		do{
    			System.out.print("请输入商品编号:");
    			num = superman.nextInt();
    			switch (num){
    			case 1:
    				System.out.println("T恤\t245.0元");
    				break;
    			case 2:
    				System.out.println("网球鞋\t570.0元");
    				break;
    			case 3:
    				System.out.println("网球拍\t320.0元");
    				break;
    			}
    			System.out.print("是否想继续,请输入y/n:");
    			str1 = superman.next();
    		}while (!str1.equals("n"));
    		System.out.println("退出程序");
    		break;
    	case "n":
    		System.out.println("退出程序");
    		break;
    	}
	}
}

结果如下：

我们也可以什么都不查看直接退出。

我们还可以只查看其中几种产品后，再退出。

3）习题3：升级版本小系统

代码如下：

import java.util.Scanner;
public class Demo5 {
    	public static void main(String[] args) {
    		Scanner superman = new Scanner(System.in);
    		System.out.println("请输入选择购买的商品编号:");
    		System.out.println("         商品列表        ");
    		System.out.println("1.T恤\t2.网球鞋\t3.网球拍");
    		System.out.println("*********************************");
    		int num;
    	int num2;
    	double buyMoney1,buyMoney2,buyMoney3;
    	double buysum = 0;
    	double discount = 0.8;
    	double payMoney;
    	double refund;
    	String str;
    	String str1;
    	System.out.print("是否想继续,请输入y/n:");
    	str = superman.next();
    	switch (str){
    	case "y":
    		System.out.println("-----------*____*-------------");
    		do{
    			System.out.print("请输入商品编号:");
    			num = superman.nextInt();
    			switch (num){
    			case 1:
    				System.out.println("T恤\t245.0元");
    				System.out.print("请输入购买数量:");
    				num2 = superman.nextInt();
    				buyMoney1 =(double) 245.0 * num2;
    				System.out.println("T恤支付的总金额为:" + buyMoney1 +"元");
    				buysum += buyMoney1;
    				break;
    			case 2:
					System.out.println("网球鞋\t570.0元");
					System.out.print("请输入购买数量:");
					num2 = superman.nextInt();
					buyMoney2 = (double) 570.0 * num2;
					System.out.println("网球鞋支付的总金额为:" + buyMoney2 +"元");
					buysum += buyMoney2;
					break;
				case 3:
					System.out.println("网球拍\t320.0元");
					System.out.print("请输入购买数量:");
					num2 = superman.nextInt();
					buyMoney3 = (double) 320.0 * num2;
					System.out.println("网球拍支付的总金额为:" + buyMoney3 +"元");
					buysum += buyMoney3;
					break;
                }
    			System.out.print("是否想继续,请输入y/n:");
    			str1 = superman.next();
    		}while (!str1.equals("n"));
    	
			if (buysum != 0){
				System.out.println("打折之前收费:" + buysum);
				buysum *= discount;
				System.out.println("金额总计:" + buysum);
				System.out.println("请输入您的实际缴费金额:");
				payMoney = superman.nextDouble();
				refund = payMoney - buysum;
				System.out.println("找钱:" + refund);
			}
    		System.out.println("退出程序");
    		break;
		case "n":
			System.out.println("退出程序");
			break;
		}
	}
}

结果如下：