Fraction

// Fractions program that does the math for user with operations of + - * /
// Renee Waggoner
// July 17, 2019
// Special Requirements: None
package fractions;
import java.util.Scanner;

public class Fraction {
    private Scanner scan = new Scanner(System.in);
    private int num=1;
    private int denom=1;

    public Fraction()
    {
        num = 1;
        denom = 1;
    }

    public Fraction(int n, int d)
    {
        // Fill in code (good to use setFraction)
        setFraction(n,d);
    }

    public void setFraction(int n, int d)
    {
        //Fill in code ... don't forget to reduce
        num = n;
        denom = d;
        reduce();
    }

    public Fraction add(Fraction op)
    {
        //Fill in code ... don't forget to reduce
        // Algebra HINT: a/b + c/d = (a*d + b*c)/(b*d)
        int greatestDenom = op.denom * denom;
        int multiplyx = greatestDenom / op.denom;
        int multiply = greatestDenom / denom;
        int d, n;
        d = op.denom * denom;
        n = (op.num * multiplyx) + (num * multiply);
        // creating new fraction
        Fraction rootDenom = new Fraction(n,d);
        return rootDenom;
    }

    public Fraction subtract(Fraction op)
    {
        //Fill in code ... don't forget to reduce
        // Algebra HINT: a/b - c/d = (a*d - b*c)/(b*d)
        int greatestDenom = op.denom * denom;
        int multiplyx = greatestDenom / op.denom;
        int multiply = greatestDenom / denom;
        int d = 0;
        int n;
        d = op.denom * denom;

        if(op.num > num)
        {
            n = (op.num * multiplyx) - (num * multiply);
        }
        else
        {
            n = (num * multiply) - (op.num * multiplyx);
        }
        // creating new fraction
        Fraction rootDenom = new Fraction(n,d);
        return rootDenom;
    }

    public Fraction multiply(Fraction op)
    {
        //Fill in code ... don't forget to reduce
        // Algebra HINT: a/b * c/d = (a*c)/ (b*d)
        int n,d;
        n = num * op.num;
        d = denom * op.denom;
        Fraction rootDenom = new Fraction(n,d);
        return rootDenom;

    }

    public Fraction divide(Fraction op)
    {
        //Fill in code ... don't forget to reduce
        // Algebra HINT: a/b / c/d = (a*d)/ (b*c)
        int n, d;
        n = num * op.denom;
        d = denom * op.num;
        Fraction rootDenom = new Fraction(n,d);
        return rootDenom;
    }

    private void reduce()
    {
        // Pseudo code:
        // set smaller = minimum ( abs(num), abs(denom));
        int smaller = Math.abs(num) < Math.abs(denom) ? num : denom;

        // Loop through the possible divisors: 2, 3, 4, ... smaller
        for(int i = 2; i <= smaller; i++)

            // For each possible divisor:
        {
            // while (num and denom are evenly divisible by divisor)
            while(num % i == 0 && denom % i == 0)
            {
                num /= i;
                denom /= i;
                smaller /= i;
            }
        }
    }
    public boolean equals(Fraction f)
    {
        // Assuming all fractions are reduced. Fill in code
        reduce();
        f.reduce();
        if (f.num == num && f.denom == denom) {
            return true;
        } else {
            return false;
        }
    }

    public String toString()
    {
        return num + "/" + denom;
    }

    public void readin(String label)
    {
        while (true) // Keep trying if bad input is received
        {
            System.out.print(label);
            String temp = scan.next();
            temp = temp.trim(); // get rid of white space at the beginning and end
            int index = temp.indexOf('/');
            if (index >= 0)
            {
                String numStr = temp.substring(0, index);
                String denomStr = temp.substring(index+1);
                int n = Integer.parseInt(numStr);
                int d = Integer.parseInt(denomStr);
                setFraction(n,d);
                return;
            }
            else
                System.out.println("Input Fraction missing / ");
        }//Keep trying until you get it right
    }

    public static void main(String[] args)
    {
        Fraction f1 = new Fraction();
        Fraction f2 = new Fraction();
        Fraction f3 = null;
        Scanner scan = new Scanner(System.in);

        while(true)
        {
            System.out.println(); // Add a blank line
            System.out.print("Enter operation: + - * / q (q ==> quit) : ");
            String input = scan.next();
            if (input.charAt(0) == 'q')
                break; // All done

            f1.readin("Enter Fraction 1: ");
            f2.readin("Enter Fraction 2: ");
            System.out.println("f1 = " + f1);
            System.out.println("f2 = " + f2);

            if (f1.equals(f2))
                System.out.println("f1 and f2 are equal");
            else
                System.out.println("f1 and f2 are not equal");

            switch (input.charAt(0))
            {
            case '+':
                f3 = f1.add(f2);
                System.out.println("f1 + f2 = " + f3);
                break;
            case '-':
                f3 = f1.subtract(f2);
                System.out.println("f1 - f2 = " + f3);
                break;
            case '*':
                f3 = f1.multiply(f2);
                System.out.println("f1 * f2 = " + f3);
                break;
            case '/':
                f3 = f1.divide(f2);
                System.out.println("f1 / f2 = " + f3);
                break;
            default:
                System.out.println("Illegal command: " + input );
                break;
            }// end of switch statement
        }// end of while loop
        System.out.println("Bye");
        scan.close();
    } // end of main
}