import java.util.Scanner;
import java.util.*;
import java.lang.Math;

public class BinaryToDecimal {
  public static void main(String[] args) {
  Scanner in = new Scanner(System.in);
    System.out.println("Please enter either a binary number as a sequence of 1's and 0's or type 'quit' to exit the program");
  String bin = in.nextLine();
  String bin2 = bin.toLowerCase();
  int len = bin2.length();
  int len2 = len;
  int dec = 0;
  String chartostring;
  int chartoint = 0;

  while (len == 0){System.out.println("Nothing was inputted, please input either 'quit' or a binary number");
  bin2 = in.nextLine();}

 if (bin2.indexOf("quit") > -1 && len == 4){
   return;}

 while (bin2.indexOf("quit") > -1 && len != 4)
 {System.out.println("Input can't have letters besides specifically entering the word 'quit' to exit the program");
  bin2 = in.nextLine();}

if (bin2.indexOf("quit") == -1){
  if (bin2.matches("\\d[01]+") || bin2.equals("1") || bin2.equals("0")) {
    do {
    chartostring = Character.toString(bin2.charAt(len-len2));
    chartoint = Integer.parseInt(chartostring);
    dec += (chartoint*((int)Math.pow(2, (len2 - 1))));
    len2--;
                       } while (len2 != 0);
  System.out.println("This is your original binary number: " + bin2);
  System.out.println("This is the converted decimal number: " + dec);
  }
  else if (!bin2.matches("\\d[01]+")) {
  System.out.println("Input can't have numbers besides 1 and 0, or any letters if you have not decided to exit with the 'quit' command");
  bin2 = in.nextLine();}
  }
  }
  }