Week 5 Second Optional HW Problem

Quadratic.java

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

public class Quadratic {

    public static void main(String[] args) {

        // version that is not interactive
        double[] roots = findRoots(1, 3, 2);

        // if we have roots
        if (roots != null)
            System.out.println(Arrays.toString(roots));
        // if we do not have roots
        else
            System.out.println("This quadratic equation has no real roots.");

        // interactive version
        findRoots();
    }

    // version that is not interactive
    public static double[] findRoots(double a, double b, double c) {
        double disc = calcDisc(a, b, c);
        System.out.println("The quadratic equation is y = " + a + "x^2 + " + b + "x + " + c);
        if (disc < 0) {
            return null;
        }
        else {
            double r1 = calcRoot1(a, b, c);
            double r2 = calcRoot2(a, b, c);
            return new double[]{r1, r2};
        }
    }

    // interactive version that requires user input
    public static void findRoots() {
        Scanner input = new Scanner(System.in);

        System.out.println("Welcome to calculating the roots of a quadratic equation!");
        System.out.println("Remember that the form of a quadratic equation is y = ax^2+bx+c");

        System.out.println("Enter the coefficient a of this quadratic equation (ex. 2.34)- ");
        String a = input.nextLine();
        double coefa = Double.parseDouble(a);

        System.out.println("Enter the coefficent b of this quadratic equation- ");
        String b = input.nextLine();
        double coefb = Double.parseDouble(b);

        System.out.println("Enter the coefficient c of this quadratic equation- ");
        String c = input.nextLine();
        double coefc = Double.parseDouble(c);

        double disc = calcDisc(coefa, coefb, coefc);

        // if discriminant is less than 0
        if (disc < 0) {
            System.out.println("This quadratic equation has no real roots. This quadratic equation has complex roots (imaginary).");
            double realPart = calcRealPart(coefa, coefb, coefc);
            double imagPart = calcImagPart(coefa, coefb, coefc);
            System.out.println("This quadratic equation has complex roots of " + realPart + " + " + imagPart + "i" + " and " + realPart + " - " + imagPart + "i");
        }
        // if discriminant is greater than or equal to 0
        else {
            System.out.println("This quadratic equation has real roots.");
            double r1 = calcRoot1(coefa, coefb, coefc);
            double r2 = calcRoot2(coefa, coefb, coefc);
            System.out.println("The roots of the quadratic equation y = " + coefa + "x^2 + " + coefb + "x + " + coefc + " are " + r1 + " and " + r2 + ".");
        }

        input.close();
    }

    // Calculates the discriminant of the quadratic equation
    public static double calcDisc(double a, double b, double c) {
        return b*b - 4*a*c;
    }

    // Calculates the first root of the quadratic equation
    public static double calcRoot1(double a, double b, double c) {
        double disc = calcDisc(a, b, c);
        return (-b + Math.sqrt(disc)) / (2*a);
    }

    // Calculates the second root of the quadratic equation
    public static double calcRoot2(double a, double b, double c) {
        double disc = calcDisc(a, b, c);
        return (-b - Math.sqrt(disc)) / (2*a);
    }

    // Calculates the real part of the root of the quadratic equation
    public static double calcRealPart(double a, double b, double c) {
        double r4= -b/(2*a);
        return r4;
    }

    // Calculates the imaginary part of the root of the quadratic equation
    public static double calcImagPart(double a, double b, double c) {
        double disc = calcDisc(a, b, c);
        return (Math.sqrt(-disc))/(2*a);
    }

}