How to check that there are no duplicates in an array? [duplicate]

Question

I'm writing an application in C# that prompts the user for data for objects of an Automobile class. One of the properties of the class for which the program prompts the user for data is ID number. If any ID number during data entry is a duplicate, the program must reprompt the user. How can I do that?

Here is the code for the class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AutomobileDemo
{
    internal class Automobile : IComparable
    {
        public int ID { get; set; }
        public string Make { get; set; }
        public int Year { get; set; }
        public double Price { get; set; }

        public override string ToString()
        {
            return ID + ": " + Make + " - " + Year + " - " + Price.ToString("C");
        }

        int IComparable.CompareTo(object obj)
        {
            Automobile anAutomible = (Automobile)obj;

            return this.ID.CompareTo(anAutomible.ID);
        }
    }
}

Here is the code for the main class:

namespace AutomobileDemo
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Automobile[] cars = new Automobile[8];
            double totalPrices = 0;

            for (int i = 0; i < cars.Length; ++i)
            {
                cars[i] = new Automobile();

                Console.Write("ID number: ");
                cars[i].ID = Convert.ToInt32(Console.ReadLine());
                Console.Write("Make: ");
                cars[i].Make = Console.ReadLine() ?? "";
                Console.Write("Year: ");
                cars[i].Year = Convert.ToInt32(Console.ReadLine());
                Console.Write("Price: ");
                cars[i].Price = Convert.ToDouble(Console.ReadLine());
                totalPrices += cars[i].Price;

                Console.WriteLine();
            }

            Array.Sort(cars);

            for (int i = 0; i < cars.Length; ++i)
                Console.WriteLine(cars[i].ToString());

            Console.WriteLine("\nTotal of all prices: " + totalPrices.ToString("C"));
        }
    }
}

Answer 1

Since you are asking about basics so I am assuming that you cannot use existing data structures or not familiar with functions hence I will just provide the snippet that should work

int id;
bool isUnique;

do
{
Console.Write("ID number: ");
id = Convert.ToInt32(Console.ReadLine());
isUnique = true; // Assume the ID is unique initially

// Check the entered ID against all previously entered IDs
for (int j = 0; j < i; j++)
{
    if (cars[j].ID == id)
    {
        Console.WriteLine("This ID has already been entered. Please enter a unique ID.");
        isUnique = false; // Mark as not unique and break the loop
        break;
    }
}

if (isUnique)
{
    cars[i].ID = id; // Set the ID only if it is unique
}

} while (!isUnique); // Keep looping until a unique ID is entered

Answer 2

You can use the Array.Exists method to check if the array already contains a matching element.

var inputID = Convert.ToInt32(Console.ReadLine());

bool duplicateId = Array.Exists(cars , element => element.ID == inputID);
if (duplicateId) {
  // Handle duplication
}
else {
  cars[i].ID = inputID;
  ...
}