CS1103 Exercise Unit 1 - Calculate the root of a quadratic equation

Posted on | In | Views
CS1103 Exercise Unit 1.

Questions

Write a program that allows the user to specify values for A, B, and C, and returns the larger of the two roots of a quadratic equation A*x*x + B*x + C = 0. Simultaneously, if an error occurs, the program should catch that error and print an error message.

1. Codes

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
import java.util.Scanner;

/**
 * SolveEquations allows the user to specify values for A, B, and C,
 * and returns the larger of the two roots of a quadratic equation A*x*x + B*x + C = 0.
 *
 * @author Zhiyao He
 */
public class SolveEquations {
    /**
     * a, b, c are the values of A, B, C entered by the user.
     * solution is the root of the quadratic equation.
     */
    public static double a;
    public static double b;
    public static double c;
    public static double solution;

    /**
     * Returns the larger of the two roots of the quadratic equation
     * A*x*x + B*x + C = 0, provided it has any roots.  If A == 0 or
     * if the discriminant, B*B - 4*A*C, is negative, then an exception
     * of type IllegalArgumentException is thrown.
     */
    public static double root(double A, double B, double C) throws IllegalArgumentException {
        if (A == 0) {
            throw new IllegalArgumentException("A can't be zero.");
        } else {
            double disc = B * B - 4 * A * C;
            if (disc < 0)
                throw new IllegalArgumentException("Discriminant < zero.");
            return (-B + Math.sqrt(disc)) / (2 * A);
        }
    }

    /**
     * Get the values of A, B, and C, then compute the root.
     * The program will continue until the user enters no.
     *
     * @param args
     */
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            while (true) {
                System.out.println("Please enter A: ");
                a = in.nextDouble();

                System.out.println("Please enter B: ");
                b = in.nextDouble();

                System.out.println("Please enter C: ");
                c = in.nextDouble();

                // compute a solution of the equation.
                try {
                    solution = root(a, b, c);
                    System.out.println("The root is: " + solution);
                } catch (IllegalArgumentException e) {
                    System.out.println("IllegalArgumentException: " + e.getMessage());
                }

                // The program will continue until the user answers no.
                System.out.println("Would you like to enter another equation? Please enter yes/no:");
                String s = in.next();
                if (s.equals("no")) {
                    System.out.println("Goodbye!");
                    break;
                }
            }
        }
    }
}

2. Outputs:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Please enter A: 
1.0
Please enter B: 
2.0
Please enter C: 
1.0
The root is: -1.0
Would you like to enter another equation? Please enter yes/no:
yes
Please enter A: 
5.0
Please enter B: 
2.0
Please enter C: 
3.0
IllegalArgumentException: Discriminant < zero.
Would you like to enter another equation? Please enter yes/no:
no
Goodbye!

Process finished with exit code 0

​

This is the ending, thanks for reading.