HexDigit2Dec.java

import java.util.Scanner;

/**
 * Created by Melissa on 19/04/2017.
 */
public class HexDigit2Dec {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a hex digit: ");
        String hexString = input.nextLine();

        // Check if the hex string has exactly one character
        if(hexString.length() != 1)
        {
            System.out.println("You must enter exactly one character");
            System.exit(1);
        }

        // Display decimal value for the hex digit
        char ch = hexString.charAt(0);
        if(ch <= 'F' && ch >= 'A') {
            int value = ch - 'A' + 10;
            System.out.println("The decimal value for hex digit " + ch + " is " + value);
        }
        else if(Character.isDigit(ch)) {
            System.out.println("The decimal value for hex digit " + ch + " is " + ch);
        }
        else {
            System.out.println(ch + " is an invalid input");
        }
    }
}