第一周周三

for循环应用程序

1到100相加

public class Name {    public static void main(String[] args) {    int sum = 0;    for (int i = 0; i < 10000; i++) {        sum+=i;    }    System.out.println(sum);    }   }

水仙花数

package com.pb.a;public class ShuiXian {    public static void main(String[] args) {        int a = 0;        int b = 0;        int c = 0;        for (int i = 100; i < 1000; i++) {             a = i/100;             b = i/10%10;             c = i%10;            if(a*a*a+b*b*b+c*c*c==i){                System.out.println(i);            }        }    }}

金字塔

package com.pb.a;public class Jin {    public static void main(String[] args) {        int lines = 5;        for (int i = 1; i <=lines; i++) {            for (int j = 0; j < lines-i; j++) {                System.out.print(" ");            }            for (int j = 0; j < i*2-1; j++) {                System.out.print("*");            }            System.out.println();        }    }}

九九乘法表

package com.pb.a;public class Chengfa {    public static void main(String[] args) {        for (int i = 1; i <= 9; i++) {            for (int j = 1; j <= i; j++) {                  System.out.print(j+"x"+i+"="+(j*i)+"\t");            }            System.out.println();        }    }}

素数求法

package com.pb.a;public class SuShu {    public static void main(String[] args) {        for (int i = 2; i <= 1000; i++) {            boolean isSuShu = true;            for (int j = 2; j < i; j++) {                if(i%j==0){                    isSuShu=false;                    break;                }            }            if(isSuShu){                System.out.println(i);            }        }    }}

求完美数

package com.pb.a;public class Perfect {    public static void main(String[] args) {        for (int i = 1; i < 1000; i++) {            int sum = 0;            for (int j = 1; j < i; j++) {                //求i的所有因子之和                if(i%j==0){                    sum+=j;                }            }            if(i==sum){                System.out.println(i);            }        }    }}

生兔子问题

package com.pb.a;public class Rabit {    public static void main(String[] args) {        int a = 1;        int b = 2;        int c = 3;        int d = 0;        for (int i = 4; i <= 20; i++) {            d = a+c;            a = b;            b = c;            c = d;        }        System.out.println(d);    }}

求1+3+7+…+(2^20-1)的结果

public class JiShu {    public static void main(String[] args) {        int sum = 0;        int m = 1;        for (int i = 1; i <21; i++) {            m = m*2;            sum = sum+m-1;         }        System.out.println(sum);    }}

求1+3+7+…+(2^20-1)

public class JiShu2 {    public static void main(String[] args) {        int sum = 0;        for (int i = 1; i < 21; i++) {            int m = 1;            m=m<<i;            sum=sum+m-1;        }        System.out.println(sum);    }}

求1-1/2+1/3-1/4+1/5…1/n的结果

public class num1 {    public static void main(String[] args) {        double sum = 0;        int n = 100;        for (int i = 1; i < n; i++) {            if(i%2==0){                sum-=1.0/i;            }else{                sum+=1.0/i;            }        }        System.out.println(sum);    }}

将一个数转换成二进制数，求1的个数

public class Rabit {    public static void main(String[] args) {        int a = 7;        int num = 0;        while(a!=0){            if(a%2==1){                num++;            }            a=a/2;        }        System.out.println(num);    }}