编程练习，简单练习

1.请输入一个数，判断这个数是偶数还是奇数，如果是偶数，请判断从1到该数是3的倍数的有哪些，如果是奇数，请判断从1到该数5的倍数有哪些；

package LianXi;

import java.util.Arrays;
import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个数：");
        int x = scanner.nextInt();
        if (x % 2 == 0){
            System.out.println("这是个偶数!");
            int count = 1;
            for (int a = count; a <= x; a++){
                if (a % 3 == 0){
                    System.out.println("从1到该数是3的倍数有：" + a);
                }
            }
        }else if (x % 1 == 0 && x != 1){
            System.out.println("这是个奇数!");
            int count = 1;
            for (int a = count; a <= x; a++){
                if (a % 5 == 0){
                    System.out.println("从1到该数是5的倍数有:" + a);
                }
            }
        }
    }
}

2.设计一个程序，完成（英雄）商品的购买，展示商品信息（折扣）-->输入商品价格-->输入购买数量-->提示付款-->输入付款金额-->打印购买小票（扩展）；

package LianXi;

import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double a = 30;
        double b = 40;
        double c = 50;
        System.out.println("商品信息为：");
        System.out.println("a英雄：5折！" + " " + "b英雄：4折!" + " " + "c英雄：3折!");
        System.out.print("请输入要购买的英雄价格：");
        double x = scanner.nextDouble();
        System.out.print("请输入购买英雄数量：");
        int y = scanner.nextInt();
        System.out.print("请付款:");
        double z = scanner.nextDouble();
        if (x == a ){
            double j = z - y * a * 0.5;
            System.out.println("----------购物小票----------：");
            System.out.println("     您总共支付：" + z + "元");
            System.out.println("     您购买的英雄数量为：" + y + "个");
            System.out.println("     英雄价格为：" + x);
            System.out.println("     该英雄折扣为：" + "5折");
            System.out.println("     英雄最终价格为：" + a * 0.5 * y);
            System.out.println("     找零：" + j);
        }else if (x == b){
            double k = z - y * b * 0.4;
            System.out.println("----------购物小票----------：");
            System.out.println("     您总共支付：" + z + "元");
            System.out.println("     您购买的英雄数量为：" + y + "个");
            System.out.println("     英雄价格为：" + x);
            System.out.println("     该英雄折扣为：" + "4折");
            System.out.println("     英雄最终价格为：" + b * 0.4 * y);
            System.out.println("     找零：" + k);
        }else if (x == c){
            double l = z - y * c * 0.3;
            System.out.println("----------购物小票----------：");
            System.out.println("     您总共支付：" + z + "元");
            System.out.println("     您购买的英雄数量为：" + y + "个");
            System.out.println("     英雄价格为：" + x);
            System.out.println("     该英雄折扣为：" + "3折");
            System.out.println("     英雄最终价格为：" + c * 0.3 * y);
            System.out.println("     找零：" + l);
        }else {
            System.out.println("余额不足！！");
        }
    }
}

3.输入三边的长度，求三角形的面积和周长（海伦公式）

package LianXi;

import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入三角形的三条边：");
        double a = scanner.nextDouble();
        double b = scanner.nextDouble();
        double c = scanner.nextDouble();
        if (a + b <= c || a + c <= b || b + c <= a){
            System.out.println("这不是个三角形");
        }else{
            double l = a + b + c;
            double p = l / 2;
            double s = Math.sqrt(p * (p - a) * (p - b) * (p - c));
            System.out.println("三角形周长为：" + l);
            System.out.println("三角形面积为：" + s);
        }
    }
}

4.输入宽和高，求矩形的面积和周长；

package LianXi;

import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入矩形的宽和高：");
        double a = scanner.nextDouble();
        double b = scanner.nextDouble();
        if (a == b){
            System.out.println("矩形的面积为：" + a * a);
            System.out.println("矩形的周长为：" + 4 * a);
        }else {
            System.out.println("矩形的面积为：" + a * b);
            System.out.println("矩形的周长为：" + (2 * a + 2 * b));
        }
    }
}

5.0~100和，循环求：

package LianXi;

import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int sum = 0;
        for (int i = 1; i <= 100; i++){
            sum += i;
        }
        System.out.println("0~100的和为：" + sum);
    }
}

6.打印100行“hello word!”,三种循环方式打印；

package LianXi;

public class lianxi {
    public static void main(String[] args) {
        //打印一百行hello word!，for循环，先做判断，再循环，可能一次都不执行
        for (int i = 1; i <=100; i++){
            System.out.println("hello word!");
        }
        //while循环，先做判断，再循环，可能一次都不执行
        int a = 1;
        while (a <= 100){
            System.out.println("hello word!");
            a++;
        }
        //do-while循环，先执行一次，再判断条件，所以至少会执行一次
        int a = 1;
        do {
            System.out.println("hello word!");
            a++;
        }while(a <= 100);
    }
}

7.打印三角形：

（1）打印正反等腰直角三角形：

package LianXi;
import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //直角在左上角
       for (int i = 1; i <= 5; i++){
           for (int j = i; j <= 5; j++){
               System.out.print("*" + " ");
           }
           System.out.println();
       }

        //直角在左下角
        for (int i = 1; i <= 5; i++){
           for (int j = 5 - i; j < 5; j++){
               System.out.print("*" + " ");
           }
           System.out.println();
       }

        //直角在右下角
        for (int i = 1; i <= 5; i++){  //外层控制层数
            for (int j = 1; j <= 5 - i ; j++){   //内层控制每行打印的星数，即列数
                System.out.print(" " + " ");
            }
            for (int k = 1; k <= i; k++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }
        //直角在右上角
        for (int i = 0; i <= 5; i++){  //外层控制层数
            for (int j = 0; j < i ; j++){   //内层控制每行打印的星数，即列数
                System.out.print(" " + " ");
            }
            for (int k = 1; k <= 5 - i; k++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }

        //通用打印
        System.out.println("请输入要打印的层数：");
        int layer = scanner.nextInt();
        for (int i = 1; i <= layer; i++){
            for (int j = 1; j <= i; j++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }

    }
}

（2）：打印矩形：

package LianXi;

public class lianxi {
    public static void main(String[] args) {
        for (int i = 1; i <= 4; i++){  //外层控制层数
            for (int j = 1; j <= 4 ; j++){   //内层控制每行打印的星数，即列数
                System.out.print("*" + " ");
            }
            System.out.println();
        }
    }
}

（3）：打印平行四边形：

package LianXi;

public class lianxi {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++){  //外层控制层数
            for (int j = 1; j <= 5 - i ; j++){   //内层控制每行打印的星数，即列数
                System.out.print(" " + " ");
            }
            for (int k = 1; k <= 5; k++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }
    }
}

（4）：打印等腰三角形：

package LianXi;

import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要打印的层数：");
        int index = scanner.nextInt();
        for (int i = 1; i <= index; i++){
            for (int j = 1; j <= index - i; j++){
                System.out.print(" " + " ");
            }
            for (int k = 1; k <= 2 * i - 1; k++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }
    }
}

（5）：打印九九乘法表

//打印99乘法表
        for (int i = 1; i <= 9; i++){
            for (int j = 1; j <= i; j++){
                System.out.print(j + "*" + i + "=" + i * j + "\t");
            }
            System.out.println();
        }

（6）：打印

*                    *
* *                * *
* * *     和     * * *
* *                * *
*                    *

package LianXi;

public class lianxi {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++){
            for (int j = 1; j <= i && j <= 6 - i; j++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }
        for (int i = 1; i <= 5; i++){
            for (int j = 1; j <= Math.abs(i - 3); j++){
                System.out.print(" " + " ");
            }
            for (int k = 1; k <= i && k <= 6 - i; k++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }
    }
}

（9）：打印菱形以及空心菱形

  *                   *
 * *                 * *
* * *       和      *   *
 * *                 * *
  *                   *

package LianXi;

public class lianxi {
    public static void main(String[] args) {
        //菱形
        for (int i = 1; i <= 5; i++){
            for (int j = 1; j <= Math.abs(i - 3); j++){
                System.out.print(" ");
            }
            for (int k = 1; k <= i && k <= 6 - i; k++){
                System.out.print("*" + " ");
            }
            System.out.println();
        }
        //空心菱形
        
    }
}

8.判断质数：

package LianXi;

import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个数字：");
        int a = scanner.nextInt();
        boolean flag = true;
        for (int i = 2; i < a; i++){
            if (a % i == 0){
                flag = false;
                break;
            }
        }
        if (flag){
            System.out.println(a + "是质数！");
        }else {
            System.out.println(a + "是合数！");
        }
    }
}

9.打印一个表格，根据用户输入的数：

1                1*1                1*1*1

2                2*2                2*2*2

...                ...                ......

n                n*n                n*n*n

package LianXi;

import java.util.Scanner;

public class lianxi {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入数字：");
        int a = scanner.nextInt();
        for (int i = 1; i <= a; i++){
            System.out.println(i + "\t" + i + "的平方=" + i * i + "\t" + i + "的立方=" + i * i * i);
        }
    }
}

10.