Help please with debugging program (simple error i think)

Question

This code will compile/execute fine, but when I run it through an automatic marking system which forces it to read lines from a text file, it runs into errors.
It seems as if it reads in the first line fine, and does what it has to do it to it, but it errors out once it tries to read the 2nd line. Can anybody see any reasons for this?
The auto mark system returns this error:
FAIL: java Mind 0113 < input.txt
Expected: Guess the 4 digit secret, or type ? to give up
Expected: > Golds 1, silvers 0
Expected: > Golds 3, silvers 0
Expected: > Correct, using 3 guesses
Actual: Guess the 4 digit secret, or type ? to give up
Actual: > Golds 1, silvers 0
Actual: >
Expected: no error output
Error: Exception in thread "main" java.util.NoSuchElementException: No line found
Error:      at java.util.Scanner.nextLine(Scanner.java:1471)
Error:      at Mind.begin(Mind.java:113)
Error:      at Mind.main(Mind.java:32)
NO NEWLINE AT END OF LAST LINE
And here is my code:
//Mind game
import java.io.*;
import java.util.*;
import java.util.Random;
class Mind
     public static void main(String[] args){
          Mind program = new Mind();
          if(args.length > 2)
               System.err.println("Invalid");
          else if(args.length == 2)
               program.start(args[0],args[1]);
          else if(args.length == 0)
               Random number = new Random();
               int n1 = number.nextInt(10);
               int n2 = number.nextInt(10);
               int n3 = number.nextInt(10);
               int n4 = number.nextInt(10);
               String sec=""+n1+n2+n3+n4;
               program.begin(sec);     
          else
               program.begin(args[0]);
     void start(String s1,String s2)
          int length = 4;
          int a = 0;
          int b = 0;
          if((s1.length() == length) && (s2.length() == length))
               try
                    a = Integer.parseInt(s1);
                    b = Integer.parseInt(s2);
               catch (NumberFormatException exc)
      System.err.println("Invalid - Incorrect formatting");
      System.exit(1);
          Gold name = new Gold();
          int[] result=name.gold(s1,s2);
          System.out.println("Golds " + result[0] + ", silvers " + result[1]);
          else
               System.err.println("Invalid numbers");
     void begin(String s1)
          int i = 1;
          char word[] = s1.toCharArray();
          int Length = 4;
          int a = 0;
          int g = 0;
          if((word[0] == '-') && (word[1] == 's'))
               Random number = new Random();
               int n1 = number.nextInt(10);
               int n2 = number.nextInt(10);
               int n3 = number.nextInt(10);
               int n4 = number.nextInt(10);
               String secret=""+n1+n2+n3+n4;
               System.out.println(secret);
          else if(s1.length() == Length)
               System.out.println("Guess the 4 digit secret, or type ? to give up");
               try
                    a = Integer.parseInt(s1);
               catch (NumberFormatException exc)
      System.err.println("Invalid - Incorrect formatting");
      System.exit(1);
    do
    String prompt = "> ";
    System.out.print (prompt);
    System.out.flush();
    Scanner input = new Scanner(System.in);
    String line = input.nextLine();
    char key[] = s1.toCharArray();
    char guess[] = line.toCharArray();
    if(guess[0] == '?')
         System.out.println("The secret was " + s1 );
         System.exit(1);
    if(line.length() == Length)
         try
              g = Integer.parseInt(line);
         catch (NumberFormatException exc)
      System.err.println("Please type 4 digits or ? to give up");
      i--;
    if(line.equals(s1))
         System.out.println("Correct, using " + i + " guesses");
         break;
    Gold name1 = new Gold();
     int[] result1=name1.gold(line,s1);
     System.out.println("Golds " + result1[0] + ", silvers " + result1[1]);
    else
    System.out.println("Please type 4 digits or ? to give up"); 
    i--;
     i++;
          } while(i < 2000);
}

Answer 1

The line:
String line = input.nextLine();is being invoked repetitively within the do loop and you are not checking if there is a next line. You have to test the result of input.hasNextLine() and break out of your loop when it returns false.