126讲while、do while

• while循环流程图

输出10句 “你好韩顺平教育”

public class While01{
    public static void main(String[] args){
        int i = 1;
        while(i <=10){
            System.out.println("hello,DearL" + i);
            i++;//如果没有这个变量迭代，会编程一个无限循环（死循环）。
        }
        System.out.println("推出while,继续。。");
    }
}

while循环控制

public class WhileExercise{
    public static void main(String[] args){
        //思路分析：打印1-100之间所有能被3整除的数，使用while语句
        //1.初始化一个int 变量 a， 判断a % 3 == 0 ?,为0就打印输出
        int a = 0;
        while(a <=100){
            if(;a%3 == 0;){
                System.out.println("diliver 3 is a Integar =" + a);
            }
            a++;
        }
        System.out.println("done");

        System.out.println("\t ======================");
        //打印40-400之间所有的偶数，使用while练习  
        //化繁为简，先死后活
        //思路分析
        //1.先打印40-200之间的所有偶数
        int b = 40;
        while(b <= 200){
            if(b%2 == 0){
            System.out.println("b=" + b);
            }
            b++;
        }
        System.out.println("Done");
    }
}

do..while循环

要账

while循环：先问还不还钱？不还钱打一顿，再问还不还钱？直到还钱就不打了。

do..while循环：先打一顿，再问还不还钱？不还钱再打一顿，直到还钱才不打

• do while流程图

• 练习题：用do while输出10句Hello,DearL

public class DoWhile{
    public static void main(String[] args){
        int a = 1;
        do{
            System.out.println("Hello,DearL" + a);
            a++;
        }while(a <= 10);

    }
}

课堂练习

public class DoWhileExercise{
    public static void main(String[] args){
        int a = 1;
        int sum = 0;
        do{
            System.out.println(a);
            ++a;
            sum += a;
        }while(a <= 100);
        System.out.println("sum=" + sum);
    }
}

public class DoWhileExercise01{
    public static void main(String[] args){
         int min = 1;
        int max = 200;
        int count = 0;
        int num = 0;
        do{
            if((count%5 == 0) && (count%3 != 0)){
                System.out.println("num =" + count);
                num++;
            }
            count++;
        }while(count <= max);
    System.out.println("num =" + num);
    }
}

import java.util.Scanner;
public class DoWhileExercise02{
    public static void main(String[] args){
        Scanner myScanner = new Scanner(System.in);
    char answer = ' ';
        do{
            System.out.println("fxxxu");
            System.out.println("give back money ? Y/N?");
            answer = myScanner.next().charAt(0);

        }while(answer != 'Y');
    System.out.println("done");

    }
}

//判断条件很关键！！！ while(answer != 'y');