Evil Alien

Book: Computer Spacegames

Author: Usborne Publishing
Translator: Marcus Medina

Story

Somewhere in the deepest, blackest space lurks Elron, the Evil Alien. You have managed to deactivate all but his short-range weapons, but he can still make his ship invisible. Elron hides somewhere within a three-dimensional grid displayed on your screen. You have four space bombs and must guess his position to blast him out of space before he captures you. Can you succeed?

Pseudocode

START
   INITIALIZE grid size and attempts
   RANDOMIZE alien's X, Y, and D positions
   LOOP for allowed attempts
      GET player's guess for X, Y, and D
      IF guess matches alien's position THEN
         PRINT success message
         EXIT
      ELSE
         GIVE directional feedback (NORTH, SOUTH, etc.)
         GIVE distance feedback (TOO FAR or NOT FAR ENOUGH)
   END LOOP
   PRINT failure message if unsuccessful
END

Flowchart

flowchart TD
    Start[Start] --> Init["Initialize grid size and attempts"]
    Init --> Randomize["Randomize alien's X, Y, and D positions"]
    Randomize --> AttemptsLoop["For each allowed attempt"]
    AttemptsLoop --> PlayerGuess["Get player's X, Y, D guesses"]
    PlayerGuess --> CheckMatch["Does guess match alien's position?"]
    CheckMatch -->|Yes| Success["Print success message"]
    CheckMatch -->|No| Feedback["Give directional and distance feedback"]
    Feedback --> AttemptsLoop
    AttemptsLoop -->|After all attempts| Failure["Print failure message"]
    Success --> End["End"]
    Failure --> End

Code

Pages

Evil Alien, sida 9 — Usborne Computer Spacegames
Evil Alien, sida 10 — Usborne Computer Spacegames

ZX-81 BASIC 
10 CLS
20 LET S=10
30 LET G=4
40 LET X=INT(RND*S)
50 LET Y=INT(RND*S)
60 LET D=INT(RND*S)
70 FOR I=1 TO G
80 PRINT "X POSITION (0 TO 9)? "
85 INPUT X1
90 PRINT "Y POSITION (0 TO 9)? "
100 INPUT Y1
110 PRINT "DISTANCE (0 TO 9)? "
120 INPUT D1
130 IF X1=X AND Y1=Y AND D1=D THEN GOTO 300
140 PRINT "SHOT WAS ";
150 IF Y1>Y THEN PRINT "NORTH";
160 IF Y1<Y THEN PRINT "SOUTH";
170 IF X1>X THEN PRINT "EAST";
180 IF X1<X THEN PRINT "WEST";
190 PRINT
200 IF D1>D THEN PRINT "TOO FAR"
210 IF D1<D THEN PRINT "NOT FAR ENOUGH"
220 NEXT I
230 PRINT "YOUR TIME HAS RUN OUT!!!"
240 STOP
300 PRINT "*BOOM* YOU GOT HIM!"
C# 
using System;


class EvilAlien
{
    static void Main()
    {
        Random rnd = new Random();
        int gridSize = 10;
        int attempts = 4;
        int alienX = rnd.Next(0, gridSize);
        int alienY = rnd.Next(0, gridSize);
        int alienD = rnd.Next(0, gridSize);


        Console.WriteLine("EVIL ALIEN");


        for (int i = 0; i < attempts; i++)
        {
            int playerX;
            do
            {
                Console.Write("X POSITION (0 TO 9)? ");
            } while (!int.TryParse(Console.ReadLine(), out playerX) || playerX < 0 || playerX > 9);


            int playerY;
            do
            {
                Console.Write("Y POSITION (0 TO 9)? ");
            } while (!int.TryParse(Console.ReadLine(), out playerY) || playerY < 0 || playerY > 9);


            int playerD;
            do
            {
                Console.Write("DISTANCE (0 TO 9)? ");
            } while (!int.TryParse(Console.ReadLine(), out playerD) || playerD < 0 || playerD > 9);


            if (playerX == alienX && playerY == alienY && playerD == alienD)
            {
                Console.WriteLine("*BOOM* YOU GOT HIM!");
                return;
            }


            Console.Write("SHOT WAS ");
            if (playerY > alienY) Console.Write("NORTH ");
            if (playerY < alienY) Console.Write("SOUTH ");
            if (playerX > alienX) Console.Write("EAST ");
            if (playerX < alienX) Console.Write("WEST ");
            Console.WriteLine();


            if (playerD > alienD)
                Console.WriteLine("TOO FAR");
            else if (playerD < alienD)
                Console.WriteLine("NOT FAR ENOUGH");
        }


        Console.WriteLine("YOUR TIME HAS RUN OUT!!!");
    }
}
Python 
import random


def main():
    grid_size = 10
    attempts = 4
    alien_x = random.randint(0, grid_size - 1)
    alien_y = random.randint(0, grid_size - 1)
    alien_d = random.randint(0, grid_size - 1)


    print("EVIL ALIEN")


    for _ in range(attempts):
        player_x = int(input("X POSITION (0 TO 9)? "))
        player_y = int(input("Y POSITION (0 TO 9)? "))
        player_d = int(input("DISTANCE (0 TO 9)? "))


        if player_x == alien_x and player_y == alien_y and player_d == alien_d:
            print("*BOOM* YOU GOT HIM!")
            return


        print("SHOT WAS", end=" ")
        if player_y > alien_y:
            print("NORTH", end=" ")
        if player_y < alien_y:
            print("SOUTH", end=" ")
        if player_x > alien_x:
            print("EAST", end=" ")
        if player_x < alien_x:
            print("WEST", end=" ")
        print()


        if player_d > alien_d:
            print("TOO FAR")
        elif player_d < alien_d:
            print("NOT FAR ENOUGH")


    print("YOUR TIME HAS RUN OUT!!!")


if __name__ == "__main__":
    main()
Java 
import java.util.Scanner;
import java.util.Random;


public class EvilAlien {
    public static void main(String[] args) {
        Random rnd = new Random();
        int gridSize = 10;
        int attempts = 4;
        int alienX = rnd.nextInt(gridSize);
        int alienY = rnd.nextInt(gridSize);
        int alienD = rnd.nextInt(gridSize);


        System.out.println("EVIL ALIEN");


        Scanner scanner = new Scanner(System.in);


        for (int i = 0; i < attempts; i++) {
            System.out.print("X POSITION (0 TO 9)? ");
            int playerX = scanner.nextInt();


            System.out.print("Y POSITION (0 TO 9)? ");
            int playerY = scanner.nextInt();


            System.out.print("DISTANCE (0 TO 9)? ");
            int playerD = scanner.nextInt();


            if (playerX == alienX && playerY == alienY && playerD == alienD) {
                System.out.println("*BOOM* YOU GOT HIM!");
                return;
            }


            System.out.print("SHOT WAS ");
            if (playerY > alienY) System.out.print("NORTH ");
            if (playerY < alienY) System.out.print("SOUTH ");
            if (playerX > alienX) System.out.print("EAST ");
            if (playerX < alienX) System.out.print("WEST ");
            System.out.println();


            if (playerD > alienD)
                System.out.println("TOO FAR");
            else if (playerD < alienD)
                System.out.println("NOT FAR ENOUGH");
        }


        System.out.println("YOUR TIME HAS RUN OUT!!!");
    }
}
Go 
package main


import (
    "fmt"
    "math/rand"
    "time"
)


func main() {
    rand.Seed(time.Now().UnixNano())
    gridSize := 10
    attempts := 4
    alienX := rand.Intn(gridSize)
    alienY := rand.Intn(gridSize)
    alienD := rand.Intn(gridSize)


    fmt.Println("EVIL ALIEN")


    for i := 0; i < attempts; i++ {
        var playerX, playerY, playerD int
        fmt.Print("X POSITION (0 TO 9)? ")
        fmt.Scan(&playerX)
        fmt.Print("Y POSITION (0 TO 9)? ")
        fmt.Scan(&playerY)
        fmt.Print("DISTANCE (0 TO 9)? ")
        fmt.Scan(&playerD)


        if playerX == alienX && playerY == alienY && playerD == alienD {
            fmt.Println("*BOOM* YOU GOT HIM!")
            return
        }


        fmt.Print("SHOT WAS ")
        if playerY > alienY {
            fmt.Print("NORTH ")
        }
        if playerY < alienY {
            fmt.Print("SOUTH ")
        }
        if playerX > alienX {
            fmt.Print("EAST ")
        }
        if playerX < alienX {
            fmt.Print("WEST ")
        }
        fmt.Println()


        if playerD > alienD {
            fmt.Println("TOO FAR")
        } else if playerD < alienD {
            fmt.Println("NOT FAR ENOUGH")
        }
    }


    fmt.Println("YOUR TIME HAS RUN OUT!!!")
}
C++ 
#include <iostream>
#include <cstdlib>
#include <ctime>


using namespace std;


int main() {
    srand(time(0));
    int gridSize = 10;
    int attempts = 4;
    int alienX = rand() % gridSize;
    int alienY = rand() % gridSize;
    int alienD = rand() % gridSize;


    cout << "EVIL ALIEN" << endl;


    for (int i = 0; i < attempts; i++) {
        int playerX, playerY, playerD;
        cout << "X POSITION (0 TO 9)? ";
        cin >> playerX;
        cout << "Y POSITION (0 TO 9)? ";
        cin >> playerY;
        cout << "DISTANCE (0 TO 9)? ";
        cin >> playerD;


        if (playerX == alienX && playerY == alienY && playerD == alienD) {
            cout << "*BOOM* YOU GOT HIM!" << endl;
            return 0;
        }


        cout << "SHOT WAS ";
        if (playerY > alienY) {
            cout << "NORTH ";
        }
        if (playerY < alienY) {
            cout << "SOUTH ";
        }
        if (playerX > alienX) {
            cout << "EAST ";
        }
        if (playerX < alienX) {
            cout << "WEST ";
        }
        cout << endl;


        if (playerD > alienD) {
            cout << "TOO FAR" << endl;
        } else if (playerD < alienD) {
            cout << "NOT FAR ENOUGH" << endl;
        }
    }


    cout << "YOUR TIME HAS RUN OUT!!!" << endl;
    return 0;
}

Explanation

In Evil Alien, the player guesses the coordinates (X, Y) and distance (D) of Elron’s hidden ship within a grid. The program provides directional feedback (e.g., “NORTH”) and distance feedback (e.g., “TOO FAR”) to help the player refine their guesses. The player has limited attempts to find and destroy Elron.

Challenges

  1. Grid Size: Increase or decrease the grid size to adjust difficulty.
  2. Attempt Limit: Allow the player to choose a custom number of attempts.
  3. Replayability: Add an option to restart the game after winning or losing.

These programs are adaptations of the original Usborne Computer Guides published in the 1980s. The books are free to download for personal or educational use from Usborne’s Computer and Coding Books. Programs and adaptations may not be used for commercial purposes.

Return to Computer Spacegames.