Lab 2

package sep19;
/*
 * Jacob Cacciamani
 * ID: E02073983
 * 9/19/19
 * Fall 2019
 * COSC 221
 * Section 1
 */

import java.util.Scanner;
/*
 * This program is a simple menu based program that can be used to
 * convert binary to decimal
 * and decimal to binary in the two's compliment system.
 */
public class ConverterTwosCompliment {

    public static String twosCompliment(String bin) {
        char arr[] = bin.toCharArray();
        int len = bin.length();
        boolean addOne = true;
        // Flip Bits
        for (int i = len - 1; i >= 0; i--) {
            if (arr[i] == '0')
                arr[i] = '1';
            else
                arr[i] = '0';
        }
        // Add 1
        for (int i = len - 1; i >= 0 && addOne; i--) {
                if (arr[i] == '0') {
                    arr[i] = '1';
                    addOne = false;
                }
                else {
                    arr[i] = '0';
                }
        }
        return new String(arr);
    }

    public static String convertToBinary(String dec) {
        int decimal = Integer.parseInt(dec);
        boolean negative = decimal < 0;
        String res = "";
        for (int i = 0; i < 7; i++) {
            res += (char)decimal % 2;
            decimal /= 2;
        }
        // If negative, use two's compliment, otherwise return
        return (negative) ? twosCompliment(reverseString(res + "0")) : reverseString(res + "0");
    }

    // Helper method for reversing binary strings so they aren't backwards
    public static String reverseString(String s) {
        String res = "";
        for (int i = s.length() - 1; i >= 0; i--) {
            res += s.charAt(i);
        }
        return res;
    }

    public static int convertToDecimal(String binary) {
        int sum = 0;
        int len = binary.length();
        boolean negative = false;
        if (binary.charAt(0) == '1') {
            binary = twosCompliment(binary);
            negative = true;
        }
        for (int i = 1; i < len; i++) {
            if (binary.charAt(i) == '1')
                sum += Math.pow(2, 7 - i);
        }
        return (negative) ? -sum : sum;
    }

    public static void main(String args[]) {
        int response;
        String num;
        Scanner scan = new Scanner(System.in);
        do {
            System.out.println("********************************************");
            System.out.println("Please enter 1 to convert decimal to binary");
            System.out.println("Please enter 2 to convert binary to decimal");
            System.out.println("Enter 3 to quit");
            response = scan.nextInt();
            if (response == 1) {
                System.out.println("Enter a decimal number between 127 and -128");
                num = scan.next();
                System.out.println("Your converted number is: " + convertToBinary(num));
            }
            else if (response == 2) {
                System.out.println("Enter an 8-bit binary string");
                num = scan.next();
                System.out.println("Your converted number is: " + convertToDecimal(num));
            }
        } while(response == 1 || response == 2);
        System.out.println("Goodbye!");
        scan.close();
    }
}
/*
********************************************
Please enter 1 to convert decimal to binary
Please enter 2 to convert binary to decimal
Enter 3 to quit
1
Enter a decimal number between 127 and -128
-2
Your converted number is: 11111110
********************************************
Please enter 1 to convert decimal to binary
Please enter 2 to convert binary to decimal
Enter 3 to quit
2
Enter an 8-bit binary string
01100100
Your converted number is: 100
********************************************
Please enter 1 to convert decimal to binary
Please enter 2 to convert binary to decimal
Enter 3 to quit
3
Goodbye!
*/