Question

Write a program that prompts the user to read three positive hex integers and display their sum in both hex and decimal. Your program should prompt the user to read the number again, if the input is incorrect. You must use java.lang.NumberFormatException. (chapter12.AddThreeHexNumbers.java)

Answer 1

//AddThreeHexNumbers.java
import java.util.Scanner;
public class AddThreeHexNumbers {
    public static int hexToDecimal(String hex){
        hex = hex.toLowerCase();
        int result = 0, temp = 1;
        for(int i = hex.length()-1;i>=0;i--){
            char ch = hex.charAt(i);
            if(ch>='0' && ch<='9'){
                result = result + (ch-'0')*temp;
            }
            else if(ch=='a'){
                result = result + temp*10;
            }
            else if(ch=='b'){
                result = result + temp*11;
            }
            else if(ch=='c'){
                result = result + temp*12;
            }
            else if(ch=='d'){
                result = result + temp*13;
            }
            else if(ch=='e'){
                result = result + temp*14;
            }
            else if(ch=='f'){
                result = result + temp*15;
            }
            temp = temp * 16;
        }
        return result;
    }

    public static String decimalToHex(int n){
        String res = "";
        int reminder;
        while(n>0){
            reminder = n%16;
            if(reminder>=0 && reminder<=9){
                res = reminder +res;
            }
            else if(reminder==10){
                res="A"+res;
            }
            else if(reminder==11){
                res="B"+res;
            }
            else if(reminder==12){
                res="C"+res;
            }
            else if(reminder==13){
                res="D"+res;
            }
            else if(reminder==14){
                res="E"+res;
            }
            else{
                res="F"+res;
            }
            n = n /16;
        }
        return res;
    }

    public static boolean validateHex(String s){
        char ch;
        for(int i = 0;i<s.length();i++){
            ch = s.charAt(i);
            if(!((ch>='0' && ch<='9') || (ch>='a' && ch<='f'))){
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int sum = 0;
        String hex;

        int i = 0;
        while(i<3){
            System.out.print("Enter hex value: ");
            hex = scan.next().toLowerCase();
            if(validateHex(hex)) {
                sum += hexToDecimal(hex);
                i++;
            }
            else{
                System.out.println("Invalid input");
            }
        }

        System.out.println("Sum in decimal: "+sum);
        System.out.println("Sum in hexa decimal: "+decimalToHex(sum));
    }
}