Why does the other player never gets its turn in my Last Stone Game (Nim) implementation?

Question

package HomePlace;

import java.util.Random;

import java.util.Scanner;

public class LastStone {
    public static boolean isValidEntry(int left, int User) {
        if (left > 0 && User < 4 && left >= User) {
            return true;
        } else {
            System.out.print("Invalid entry!!");
            return false;
        }
    }

    public static int userMove(int left) {
        Scanner input = new Scanner(System.in);
        System.out.print("There are " + left + " stones. How many would you like? ");
        int User = input.nextInt();
        return User;
    }

    public static int computerMove(int left) {
        int cpuStones;
        cpuStones = generateStones();
        System.out.print("There are " + left + "stones. The computer takes" + cpuStones + " stones");
        return cpuStones;
    }

    public static int generateStones() {
        Random sr = new Random();
        int gstones = sr.nextInt(2) + 1;
        return gstones;
    }

    public static void playLastStone(int UserOrCpu) {
        Scanner input = new Scanner(System.in);
        if (UserOrCpu % 2 == 1) {
            System.out.println("The Computer beats the User!");
        } else {
            System.out.println("The User beats the Computer!");
        }
    }

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Random r = new Random();
        int left = r.nextInt(16) + 15;
        int UserOrCpu = 1, User = 1, temp;
        while (true) {
            if (UserOrCpu % 2 == 1) {
                User = userMove(left);
                if (isValidEntry(left, User)) {
                    if (left == User) {
                        playLastStone(UserOrCpu);
                        break;
                    }
                    left -= User;
                } else {
                    continue;
                }
            } else {
                computerMove(left);
                temp = computerMove(left);
                if (left <= temp) {
                    playLastStone(UserOrCpu);
                    break;
                } else {
                    left -= temp;
                }
            }
        }
        UserOrCpu += 1;
    }
}

My computer player cpu never takes its turn in my implementation of the Last Stone game or Nim.

I found similar questions but none helped with solving my problem.

I debugged my code line by line but couldn't figure out why my second } else { in my main method is never executed?

                    left -= User;
                } else {
                    continue;
                }
            } else { // why is it never executed?

Answer 1

In your given code, your main method actually reduces itself to

    public static void main(String[] args) {
        Random r = new Random();
        int left = r.nextInt(16) + 15;
        int userOrCpu = 1, user;
        while (true) {
            user = userMove(left);
            if (isValidEntry(left, user)) {
                if (left == user) {
                    playLastStone(userOrCpu);
                    break;
                }
                left -= user;
            }
        }
    }

And so it's now clear that your computer player cpu never gets its turn.

The problem is that your UserOrCpu += 1; assignment isn't in the right scope, and so doesn't have any effect.

The "fixed" main method should look like this

    public static void main(String[] args) {
        Random r = new Random();
        int left = r.nextInt(16) + 15;
        int UserOrCpu = 1, User = 1, temp;
        while (true) {
            if (UserOrCpu % 2 == 1) {
                User = userMove(left);
                if (isValidEntry(left, User)) {
                    if (left == User) {
                        playLastStone(UserOrCpu);
                        break;

                    }
                    left -= User;
                } else {
                    continue;
                }
            } else {
                computerMove(left);
                temp = computerMove(left); // executes computer move a 2nd time?
                if (left <= temp) {
                    playLastStone(UserOrCpu);
                    break;

                } else {
                    left -= temp;
                }
            }
            UserOrCpu += 1;
        }
    }

Hint: Get yourself an IDE (like IntelliJ) for writing code. Such a code editor will indicate "obvious" problems with your code immediately.