package welcome;

import java.util.Scanner;

/*

 * 代数问题:求解2x2线性方程

 */

public class ComputeLinearEquation {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.print("Enter a, b, c,  d,  e, f: ");

        double a = in.nextDouble();

        double b = in.nextDouble();

        double c = in.nextDouble();

        double d = in.nextDouble();

        double e = in.nextDouble();

        double f = in.nextDouble();

        double x = 0;

        double y = 0;

        if (a * d - b * c != 0) {

            x = (e * d - b * f) / (a * d - b * c);

            y = (a * f - e * c) / (a * d - b * c);

        } else {

            System.out.println("The equation has no solution");

            System.exit(0);

        }

        System.out.println("x is " + x + " and y is " + y);

    }

}

package welcome;

import java.util.Scanner;

/*

 * 游戏:学习加法

 */

public class TestAddition {

    public static void main(String[] args) {

        int a = (int)(Math.random() * 100);

        int b = (int)(Math.random() * 100);

        Scanner in = new Scanner(System.in);

        System.out.print("What is " + a + " add " + b + " ? ");

        int guess = in.nextInt();

        if(a + b == guess){

            System.out.println("true");

        }else{

            System.out.println("false");

        }

    }

}

package welcome;

import java.util.Scanner;

/*

 * 计算一个三角形的周长

 */

public class ComputeGirth {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.print("Enter three sides of a triangle: ");

        double a = in.nextDouble();

        double b = in.nextDouble();

        double c = in.nextDouble();

        double G = 0;

        if(a + b > c && a + c > b && b + c > a){

            G = a + b + c;

        }else{

            System.out.println("The input is illegal");

            System.exit(0);

        }

        System.out.println("The triangle has a circumference of " + G);

    }

}