Java program for calculating fractions

Question

The purpose of the program is to get two user inputs for a fraction, receive a operator from the user, and then to get two more user inputs for a second fraction. The program mu

Answer 1

UPDATE:

Be aware that this is my no means complete and/or the best solution, but at least it should take you in the right direction. You will still have to reduce fractions and do some other tweaks.

import java.math.BigInteger;
import java.util.Scanner;

public class FractionCalculator {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int n1;
        int n2;
        int d1;
        int d2;
        int n = 0;
        int d;
        char o;

        System.out.println("Enter a numerator for fraction 1: ");
        n1 = in.nextInt();
        System.out.println("Enter a denominator for fraction 1: ");
        d1 = in.nextInt();

        if (d1 > 0) {
            System.out.println();
        } else {
            System.out.println("Invalid denominator");
            System.exit(0);
        }

        System.out.println("Enter an operator: ");
        o = in.next().toCharArray()[0];
        System.out.println("Enter a numerator for fraction 2: ");
        n2 = in.nextInt();
        System.out.println("Enter a denominator for fraction 2: ");
        d2 = in.nextInt();

        if (d2 > 0) {
            System.out.println();
        } else {
            System.out.println("Invalid denominator");
            System.exit(0);
        }

        switch (o) {
            case '*':
                n = n1 * n2;
                d = d1 * d2;

                break;

            case '/':
                n = n1 * d2;
                d = n2 * d1;

                break;

            case '+':
            case '-':

                d = gcd(d1, d2);

                n1 *= d / d1;
                n2 *= d / d2;

                if(o == '+') {
                    n = n1 + n2;
                }
                else if(o == '-') {
                    n = n1 - n2;
                }

                break;
            default:
                System.out.println("Illegal Operator: " + o);
                return;
        }

        System.out.printf(" %d     %d     %d\n", n1, n2, n);
        System.out.printf("--- %c --- = ---\n", o);
        System.out.printf(" %d     %d     %d\n", d1, d2, d);
    }

    private static int gcd(int d1, int d2) {
        BigInteger gcd = new BigInteger(String.valueOf(d1)).gcd(new BigInteger(String.valueOf(d2)));
        return gcd.intValue();
    }
}