import java.util.Scanner;

public class BaseFour{
  
  public static void main(String[] args){
    
    Scanner scan = new Scanner(System.in);
    String input = "";
    
    // So long as the String input is NOT 1-60 in length,
    //    Ask the user to enter a valid base-4 number up to 60 digits
    //    Save the next line of user input to the variable "input"




    
    
    // If the input string is NOT base-4, tell the user "Bad input!"
    // Otherwise, tell the user "You entered [numeric value of input]"
    // You can call the methods like so:
    //      isBaseFour(input)      This will give you a true or false value
    //      baseFourValue(input)   This will give you a long value



    
  }
  
  private static boolean isBaseFour(String input){
    

    // Go over each character of input
    //      If that single character is NOT '0' or'1' or '2' or '3', return false immediately
    // If you finish going through the characters, return true






    return true;
  }
  
  private static long baseFourValue(String input){
    long result;

    // To start, the exponent is 0 and the next position in 
    // in the input string is the string length minus one.  
    // You already have a long variable to hold your result.







    // While the exponent is smaller than the string length, 
    //     Get the character at the next position in the input string
    //        and store it in a char variable
    //     Subtract '0' (not 0) from that character and multiply 
    //         the result of that subtraction by (long) Math.pow(4, exponent)
    // When the loop is finished, assign the result to the variable "result"






    
    return result;
  }
  
}

1. Get a String of input from the user.
2. Depending on whether the input is valid, announce the number's value; otherwise, let the user know it is bad input.
3. Write a method to verify whether or not the user's input string is valid.
4. Write a method to calculate the value of the user's input string.

Program output examples:

Enter a valid base-4 number up to 30 digits long:
10131012131
You entered 1167773

Enter a valid base-4 number up to 30 digits long:
120132201
You entered 100257

Enter a valid base-4 number up to 30 digits long:
10121010140013
Bad input!