Java Console Guess The Number Game

Question

I was given a homework assignment to code a console Guess the Number Game, where the user should guess a random number. Also, I had to code a simple menu with switch where I can change a random number origin/bound and attempts amount.

Please, give me some tips how could I improve the code and where I'm wrong.

P.S. I must not use classes / methods etc. Only Control Flow Statements.

import java.util.Scanner;
import java.util.concurrent.ThreadLocalRandom;

public class Main {
    public static void main(String[] args) {
        var scanner = new Scanner(System.in);
        var origin = 0;
        var bound = 100;
        var attempts = 10;

        System.out.println("Guess the Number Game!");

        while (true) {
            System.out.println();
            System.out.println("1. Start new game.");
            System.out.println("2. Change origin (" + origin + ").");
            System.out.println("3. Change bound (" + bound + ").");
            System.out.println("4. Change attempts amount (" + attempts + ").");
            System.out.println("5. Quit.");
            System.out.println();

            switch (Integer.parseInt(scanner.nextLine())) {
                case 1:
                    var number = ThreadLocalRandom.current().nextInt(origin, bound);
                    var currentAttempts = attempts;
                    System.out.println("Guess the number between " + origin + " and " + bound + "!");
                    while (currentAttempts > 0) {
                        System.out.println(currentAttempts-- + " attempts left:");
                        var input = Integer.parseInt(scanner.nextLine());
                        if (input == number)
                            break;
                        else
                            System.out.println("The number is " + (input < number ? "greater" : "less") + " than yours.");
                    }
                    if (currentAttempts > 0)
                        System.out.println("You win! Congratulations!");
                    else {
                        System.out.println("You loose! Better luck next time!");
                        System.out.println("The number was " + number);
                    }
                    break;
                case 2:
                    while (true) {
                        System.out.println("Enter new origin:");
                        int newOrigin = Integer.parseInt(scanner.nextLine());
                        if (newOrigin < bound) {
                            origin = newOrigin;
                            break;
                        } else
                            System.out.println("Origin should be less than bound. Try again.");
                    }
                    break;
                case 3:
                    while (true) {
                        System.out.println("Enter new bound:");
                        int newBound = Integer.parseInt(scanner.nextLine());
                        if (newBound > origin) {
                            bound = newBound;
                            break;
                        } else
                            System.out.println("Bound should be greater than origin. Try again.");
                    }
                    break;
                case 4:
                    while (true) {
                        System.out.println("Enter new attempts amount:");
                        int newAttempts = Integer.parseInt(scanner.nextLine());
                        if (newAttempts > 0) {
                            attempts = newAttempts;
                            break;
                        } else
                            System.out.println("Attempts amount should be greater than 0. Try again.");
                    }
                    break;
                case 5:
                    System.out.println("Bye!");
                    return;
            }
        }
    }
}

Answer 1

Because of the 'I must not use classes / methods etc. Only Control Flow Statements' I will try to not give comments to that direction. Here are some advices

Input checking

Integer.parseInt(scanner.nextLine())

This will crash when someone enters anything but a digit (eg. 'a'). You should add exception handling for this

way to keep things going

while (true)

I would personally go for while(isRunning), as it will allow you to end the loop without the need for the "return" statement in the switch.

usage of var

var number = ThreadLocalRandom.current().nextInt(origin, bound);
int newOrigin = Integer.parseInt(scanner.nextLine());

You are mixing the usage of var and int when reading from the command line (which is technically ok) but I think consistency is also important in code.

default case

There is no default case in the switch. That would for example allow you to handle people entering number 6

changing variables in printing output

System.out.println(currentAttempts-- + " attempts left:")

This gets really tricky when you would use a logging framework and suddenly the user decides to switch of the level of logging. I would go for System.out.println is to print current values, and to change values before/after (whatever is appropriate)

coding style

if (input == number)
    break;
else
   System.out.println ...

I would advice to always put {}, even if the next line is a simple instruction. This will avoid any human reading mistakes.

eg.

if (<somecondition>)
    dosomething();
    break;
else
   System.out.println ...