Thread: Need help using Recursion in an assignment

Here is the assignment:
Overview
Write a program that reads a list of many-digit integers from a file, adds them together, and
writes the result to an output file.
You may not make any assumptions about the maximum number of digits that a number will
have. A reasonable linked-list implementation of the solution should run successfully with
the instructor’s test data on the instructor’s machine.
The format of the numbers will be the same as for valid real numbers in Java. You may
assume that scientific notation will not be used for the input (and should not be used for the
output).

Input
Your input will be in a text file containing several numbers, one to a line. An example of
what the input might look like is:
11111111111111111111111111111111111111111111111111 0
-11111111111111111111111111111111111111111111111111 1
22222222222222222222222222222222222222222222222222 22
33333333333333333333333333333333333333333333333333 333
-4


Output
Your output will be to another file, and will echo the input and give the result. Output for
the preceding input example might look like:
The sum of
11111111111111111111111111111111111111111111111111 0
+ -11111111111111111111111111111111111111111111111111 1
+ 22222222222222222222222222222222222222222222222222 22
+ 33333333333333333333333333333333333333333333333333 333
+ -4
is
35777777777777777777777777777777777777777777777777 772
Processing
The only processing requirement I am placing on this programming project is that it use a
linked list to store the numbers (and not BigInteger objects).
There is one additional major consideration in building your long number, though: the sign.
Adding negative numbers means doing subtraction and allowing for negative results.
One other suggestion I would make is that your program deal with each input number and
calculate a subtotal before processing the next number. Since you don’t know ahead of
time how many numbers you will need to process, storing them all is probably more difficult
than processing each as it is read from the input file.

import java.io.File;
import java.util.Scanner; 
import java.util.*;
import java.util.LinkedList;
 
public class Homework3 {
    public static void main(String[] args) throws Exception{
 
 
       File file = new File("linklist.txt");
 
       Scanner input = new Scanner(file); 
 
       LinkedList numbers = new LinkedList();
 
       System.out.println("The sum of ");
 
       while (input.hasNext()) {
           String num = input.nextLine();
           numbers.add(num);
           System.out.println(num); //Display ea number
       }
 
        System.out.println("is");
        System.out.println("");
 
 
           //Right here is where I need the code help!!!!!!!!!!!!!!!!!!!!!
 
       //Add the list items together one number at a time. Find out how long the string of each one is.
        input.close();
    }
}

I need help in finding out how to add these numbers in a string together

How would you do it "by hand" without a computer?

One number at a time starting from the right and if it is greater than 9 add 1 to the next numbers being added. My question is how would i put that into code. I am just lost. I know it has to do with char.At and some crazy loops but I can't figure it out.

If you're supposed to use recursion, then I doubt you'd also want to use "crazy loops". Check out the API for String and maybe Integer for useful functions.

String (Java Platform SE 6)
Integer (Java Platform SE 6)

import java.io.File;
import java.util.Scanner; 
import java.util.*;
import java.util.LinkedList;
 
public class Homework3 {
    public static void main(String[] args) throws Exception{
 
 
       File file = new File("linklist.txt");
 
       Scanner input = new Scanner(file); 
 
       LinkedList numbers = new LinkedList();
 
       System.out.println("The sum of ");
 
       while (input.hasNext()) {
           String num = input.nextLine();
           numbers.add(num);
           System.out.println(num); //Display ea number
       }
 
        System.out.println("is");
        System.out.println("");
 
 
           //Right here is where I need the code help!!!!!!!!!!!!!!!!!!!!!
 
       //Add the list items together one number at a time. Find out how long the string of each one is.
        input.close();
    }
}

What I personally don't get is why you would be using a LL in the first place to store each string and then add all the number together at one and not just process one at a time...
One word of advice, since the numbers you are dealing with are so huge I would suggest that you use a long representation for them instead of an int one.

so here's how I'd I'd approach the problem:

import java.io.File;
import java.util.Scanner; 
import java.util.*;
import java.util.LinkedList;
 
public class Homework3 {
    public static void main(String[] args) throws Exception{
 
 
       File file = new File("linklist.txt");
 
       Scanner input = new Scanner(file); 
 
       long number=0;
 
       System.out.println("The sum of ");
 
       while (input.hasNext()) {
           String num = input.nextLine().trim(); //trim(): delete eventual whitespaces
           number+=(new Long(num)).longValue();  //adding your num to number by converting it to a long (to do so you have to create a new Long() by passing num to it and then get its long value);
           System.out.println(num); //Display ea number
       }
 
        System.out.println("is");
        System.out.println("");
 
 
          System.out.println(number);
 
        input.close();
    }
}

I think you'll be able to manage creating the output file by yourself