How to fix this random number guessing game use a do-while loop program?

Question

Create a program that randomly generates a number from 1-100 and asks the user to guess it. If the number the user inputs is to low or to high display a message to tell them so. When the user guesses the random number tell the user how much tries it took him to get that number. After that ask the user if they want to do it again if the user does repeat the process with a new random number generated.

The problem is that I can't seem to figure out how to let the user do it again, it seems to display an error in code when I run the program. If anyone can help me with this issue that would be great. Thank you!

import java.util.Scanner;
import java.util.Random;
public class RandomGuess
{
    public static void main(String [] args)
    {
        Scanner keyboard = new Scanner(System.in);
        Random randy = new Random();

        //#declaring variables
        int num, count = 0;
        final int random = randy.nextInt(100);
        String input;
        char yn;

        //#random number
        System.out.println("Num = " + random);

        //#title or header
        System.out.println("Random Number Guessing Game");
        System.out.println("===========================");

        //#asking user for input
        do
        {
            System.out.print("Guess the random number " + 
                "from 1 to 100===> ");
            num = keyboard.nextInt();

            //#if the number the user entered
            //#was less than the random number
            if(num < random)
            {
                //#display this message
                System.out.println("Your guess is too low try again...");
                System.out.println();
            }
            //#if the number the user entered
            //#was less than the random number
            if(num > random)
            {
                //#display this message
                System.out.println("Your guess is too high try again...");
                System.out.println();
            }
            count++;
            if (num == random)
            {
                System.out.println("You guessed the random number in " + 
                    count + " guesses!");
                break;
            }
            do 
            {
                System.out.print("Continue? (Y or N)==> ");
                input = keyboard.nextLine();
                yn = input.charAt(0);
            }
            while(yn == 'Y' || yn == 'y');
        }
        while (num > 1 || num > 100);

    }
}

Answer 1

There are a couple of problems with your code without even seeing the error that is displayed (I've put comments in those areas):

            count++;
            if (num == random)
            {
                System.out.println("You guessed the random number in " + 
                    count + " guesses!");
                break;
            }   // You should put an else here
            do 
            {
                System.out.print("Continue? (Y or N)==> ");
                input = keyboard.nextLine();
                yn = input.charAt(0);
            }
            while(yn == 'Y' || yn == 'y');  // This will keep asking if you want to try again so long as you enter a "y"
                     // But it won't actually let you try.
                     // Why? Because if you enter a y" it will loop back to the question.   
        }
        while (num > 1 || num > 100); // This should probably be (random != num)

    }
}

Here is a revised version

            count++;
            if (num == random) {
                System.out.println("You guessed the random number in " + 
                    count + " guesses!");
            } else {
                yn = 'x';    // can be anything other than y or n
                while(yn != 'y' && yn != 'n') {
                  System.out.print("Continue? (Y or N)==> ");
                  input = keyboard.nextLine();
                  yn = input.toLowerCase().charAt(0);
                }
            }
        }
        while (num != random && yn == 'y');
    }
}

Hopefully this is enough to move you forward.

Also, please post the error message and/or a description of what it is doing wrong along with a description as to what you actually wnt it to do.

As for the exception, the problem is that scanner.nextInt does not consume the newline at the end of the numbe you entered. So, your "continue Y/N" question gets what's left over from the previous line (i.e. a new line => an empty string).

You could try this:

    num = -1;       // Initialise the number to enable the loop
    while (num <= 1 || num >= 100) {
      System.out.print("Guess the random number from 1 to 100===> ");
      String ans = keyboard.nextline();
      try {
        num = Integer.parseInt();     // Convert the string to an integer - if possible
      } catch (NumberFormatException e) {
           // If the user's input can not be converted to an integer, we will end up here and display an error message.
        System.out.println ("Please enter an integer");
      }
    }