2018-04-08Java循环

循环结构：

初始化;
while(循环条件) {
循环语句;
(更新;)
}
先判断，后执行

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        int i=1;
        while(i<=100){
            System.out.println("第"+i+"遍"+"我能行！");
            i++;
        }
            System.out.println("程序结束");
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        System.out.println("练得怎么样？(y/n)：");
        String str = input.next();
        while (!str.equals("y")){
            System.out.println("唱歌");
            System.out.println("跳舞");
            System.out.println("练琴");
            System.out.println("练得怎么样？(y/n):");
            str =input.next();
        }
        System.out.println("程序结束");
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        System.out.print("班级人数:");
        int count=input.nextInt();
        int i=1;
        int score,sum=0;
        while(i<=count){
            System.out.print("第"+i+"位学员成绩:");
            score=input.nextInt();
            sum +=score;
            i++;
        }
        System.out.print("平均成绩:"+(double)sum/count);
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        System.out.print("年份：");
        int i=2006;
        int b=80000;
        while(b<200000){
            b*=1.25;
            i++;
        }
        System.out.print("到"+i+"年，人数增长到"+b);
    }
}

do {
循环语句;
(初始化/更新)
}while(循环条件);
先执行，后判断

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        String s;
        do{
            System.out.println("唱歌");
            System.out.println("跳舞");
            System.out.println("练琴");
            System.out.print("可以吗？(y/N)");
            s =input.next();
        }while (!s.equalsIgnoreCase("y"));
            System.out.print("流程结束");
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        String name;
        do{
            System.out.println("学员姓名");
            name =input.next();
        }while (!name.equalsIgnoreCase("q"));
            System.out.print("流程结束");
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        double a;
        int b=0,count=1;
        System.out.println("\t摄氏度\t华氏温度");
        System.out.println("-----------------------------");
        do{
            a=b*9/5.0+32;
            b+=20;
            System.out.println("\t"+b+"\t"+a);
        }while (count<=10&&b<=250);
            System.out.print("流程结束");
    }
}

for(初始化;循环条件;更新){
循环语句;
}

break:从机构体中跳出
continue:结束本次循环，进入下一次循环

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        for(int i=1;i<=100;i++){
            System.out.print("第"+i+"遍，我能行");
        }
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        int sum=0,score;
        for(int i=1;i<=5;i++){
            System.out.print("第"+i+"遍，我能行");
            score=input.nextInt();
            sum+=score;
        }
        System.out.print(sum/5.0);
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        System.out.print("num");
        int num =input.nextInt();
        for(int i=1,j=num;i<=num&&j>=0;i++,j--){
            System.out.print(i+"+"+j+"="+(i+j));
        }
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        System.out.print("num:");
        int num = input.nextInt();
        int numBak = num;
        int r_digit;
        int count=0;
        while (num>0){
            num/=10;
            count++;
        }
        while(numBak>0){
            r_digit=numBak%10;
            num+=(int)r_digit*Math.pow(10, count-1);
            count--;
            numBak/=10;
        }
            System.out.print(num);
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        int sum=0;
        for(int i=1;i<=100;i++){
            if(i%3!=0){
                sum+=i; 
            }
        }
        System.out.println(sum);        
    }
}

public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        int score,sum=0;
        boolean flag=true;
        for(int i=1;i<=5;i++){
            System.out.println("第"+i+"位学员成绩");
            score=input.nextInt();
            if(score<0||score>100){
                flag=false;
                System.out.println("成绩输入错误，程序终止");
                break;  
            }
            sum+=score;
        }
        if(flag){
        System.out.println("平均分："+sum/5.0); 
        }
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        int sum=0;
        for(int i=1;i<=10;i++){
            sum+=i;
            if(sum>20){
            System.out.println(i);
            break;
            }
        }
        System.out.println(sum);
    }
}

package miao;
import java.util.Scanner;
public class Miao {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        int sum=0;
        for(int i=1;i<=10;i++){
            if(i%2==1){
            continue;
            }
            sum+=i;
        }
        System.out.println(sum);
    }
}

总结：
while和for都是先判断后执行
do··while是先执行再判断
break是结束本次循环返还上一次循环
continue是跳过该次判断条件继续执行其他条件