Question

need help with writing a program that converts i.e. binary to decimal or decimal to hexadecimal but cannot use the conversion tool built-in Java and please use the switch and write comments to understand.

Answer 1

If you have any problem with the code feel free to comment.

Program

import java.util.Scanner;

public class Test {
   public static void main(String[] args) {
       //for taking console input
       Scanner sc = new Scanner(System.in);
       int choice, value;
      
       while(true) {//infinite loop
           System.out.println("1. Binary to Decimal");
           System.out.println("2. Decimal to Hexadecimal");
           System.out.println("3. Exit");
           System.out.print("> ");
           choice = sc.nextInt(); sc.nextLine();//taking user choice
          
           switch(choice) {
           case 1://converting binary to decimal
               System.out.print("Enter Binary Number: ");
               value = sc.nextInt(); sc.nextLine();
               System.out.println("Decimal: "+binToDec(value));
               System.out.println();
               break;
              
           case 2://converting decimal to hexadecimal
               System.out.print("Enter Decimal Number: ");
               value = sc.nextInt(); sc.nextLine();
               System.out.println("Hexadecimal: "+decToHex(value));
               System.out.println();
               break;
              
           case 3://exit condition
               System.out.println("Good Bye");
               System.exit(0);
              
           default://choice doesn't match with cases
               System.out.println("Invalid Input!");
               System.out.println();
               break;
           }
       }
   }

   public static int binToDec(int binary) {
       int decimal = 0;
       int power = 0;
       while (true) {//infinte loop
           if (binary == 0) {
               break;//get out of loop when binary becomes zero
           } else {
               int temp = binary % 10;//extrating single digit from binary number
               decimal += temp * Math.pow(2, power);//adding the decimal form
               binary = binary / 10;
               power++;//increasing the power
           }
       }
       return decimal;
   }

   public static String decToHex(int decimal) {
       int remainder;
       String hex = "";//for holding hexadecimal
       //to select the value by providing the index
       char hexChars[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
      
       while (decimal > 0) {//loop that will run till decimal is greater than zero
          
           remainder = decimal % 16;
           //selecting the value from hexChar and adding it to hex
           hex = hexChars[remainder] + hex;
           decimal = decimal / 16;
       }
       return hex;
   }
}

Output