guessnumber.java

/* Guess my number game
 *
 * --A Java version of a silly game I made on my programmable
 *   calculator when I was bored in math class in 1987, with a couple of
 *   additions like input validation and computer guesses.
 *
 * Copyright (c) 2007 Matthew Helmke for the old Python 2 version
 * Copyright (c) 2025 Matthew Helmke for the Java version (this one)
 * Input handling revised 2026-10-12 with assistance from Claude Code
 *    (claude.ai/code) using the claude-opus-5-5 model
 *
 * To compile (Linux):
 *   javac guessnumber.java
 * To run:
 *   java guessnumber
 *
 * This program is free software; you can redistribute it and\or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.Random;

public class guessnumber {

    // Read one line, ending at a line feed, which is dropped. Returns null at
    // end of input when nothing is left; a last line with no line feed is still
    // returned. Scanner.nextLine and BufferedReader.readLine are not used: both
    // also end a line at a carriage return, and Scanner at U+0085, U+2028, and
    // U+2029 too, so "3", a carriage return, and "0" would read as two guesses.
    static String readLine(BufferedReader input) throws IOException {
        int c = input.read();
        if (c == -1) {
            return null;
        }
        StringBuilder line = new StringBuilder();
        while (c != -1 && c != '\n') {
            line.append((char) c);
            c = input.read();
        }
        return line.toString();
    }

    public static void main(String[] args) throws IOException {
        try (BufferedReader input = new BufferedReader(new InputStreamReader(System.in, StandardCharsets.UTF_8))) {
            Random random = new Random();
            int lowmax = 1;
            int highmax = 100;
            // Get a random number, or a fixed one from GMN_SECRET for parity testing.
            // As with a guess, the value must be all digits, and parseInt can then
            // fail only on a number too large for an int, which is out of range.
            int secretnumber = random.nextInt(highmax - lowmax + 1) + lowmax;
            String gmnSecret = System.getenv("GMN_SECRET");
            if (gmnSecret != null && gmnSecret.matches("\\d+")) {
                int gmnValue;
                try {
                    gmnValue = Integer.parseInt(gmnSecret);
                } catch (NumberFormatException e) {
                    gmnValue = Integer.MAX_VALUE;
                }
                if (gmnValue >= 1 && gmnValue <= 100) {
                    secretnumber = gmnValue;
                }
            }
            int userguess;
            int computerguess;
            int totalguesses = 0;

            // Print a description of the game, with rules, to the screen

            System.out.println("Welcome to Guess My Number!\n\nThe computer will select a random whole number between 1 and 100.\nYour goal is to guess that number. You will get a turn, then a computer\nplayer will get a turn. Each of you are aware of the other's guesses.\nThe first one to guess the number correctly will win. Try to guess in\nas few turns as possible.\n\nHere we go!\n\n");

            // the main bit
            while (true) {
                System.out.print("What is your guess? ");

                // let the user input any number they want
                // read the whole line; scanner.next() would read one word and skip empty lines
                String userguessunvalidated = readLine(input);
                if (userguessunvalidated == null) {
                    break; // end of input
                }

                // remove leading and trailing spaces and tabs
                userguessunvalidated = userguessunvalidated.replaceAll("^[ \\t]+|[ \\t]+$", "");

                // verify the guess is a whole number
                if (!userguessunvalidated.matches("\\d+")) {
                    System.out.println("Only whole numbers from 1 to 100 are allowed.\nPlease try again.\n");
                    continue;
                }

                // verify the guess is in range; the input is all digits, so parseInt
                // can fail only when the number is too large for an int, which is out of range
                try {
                    userguess = Integer.parseInt(userguessunvalidated);
                } catch (NumberFormatException e) {
                    userguess = Integer.MAX_VALUE;
                }
                if (userguess < 1 || userguess > 100) {
                    System.out.println("Only whole numbers from 1 to 100 are allowed. Your guess is out of range.\nPlease try again.\n");
                    continue;
                }

                // this is a real guess, so count it
                totalguesses++;

                // some taunts for silly errors in user guesses
                if (userguess < lowmax) {
                    System.out.println("That guess was lower than a previous guess that was too low. Pay attention!\n");
                }
                if (userguess > highmax) {
                    System.out.println("Wake up! That guess was higher than an earlier guess that was too high.\n");
                }

                // evaluate the guess
                if (userguess == secretnumber) {
                    System.out.println("\n*********************************************\n   Your guess is correct! Congratulations!\n   It took " + totalguesses + " total guesses.\n*********************************************\n");
                    return;
                } else if (userguess > secretnumber) {
                    System.out.println("Your guess is too high.\n");
                    if (userguess <= highmax) {
                        highmax = userguess - 1;
                    }
                } else {
                    System.out.println("Your guess is too low.\n");
                    if (userguess >= lowmax) {
                        lowmax = userguess + 1;
                    }
                }

                // computer uses the midpoint (binary search) within current bounds
                computerguess = (lowmax + highmax) / 2;
                totalguesses++;

                if (computerguess == secretnumber) {
                    System.out.println("**********************************************\n   The computer's guess of " + computerguess + " is correct!\n   It took " + totalguesses + " total guesses.\n**********************************************\n");
                    return;
                } else if (computerguess > secretnumber) {
                    System.out.println("The computer guessed " + computerguess + " and that was too high.\nPlease try again.\n");
                    highmax = computerguess - 1;
                } else {
                    System.out.println("The computer guessed " + computerguess + " and that was too low.\nPlease try again.\n");
                    lowmax = computerguess + 1;
                }

                // more taunts and a forced guess limit
                if (totalguesses == 8) {
                    System.out.println("\nThis is a hard number, isn't it?\n");
                } else if (totalguesses == 10) {
                    System.out.println("\nWow! You are really bad at this.\n");
                } else if (totalguesses >= 12) {
                    System.out.println("\nYou're taking too long, I can't handle it any more.\n\nG A M E   O V E R\n");
                    return;
                }
            }
        }
    }
}