Question

This code works for me except it only checks for a duplicate once, and if the user enters the same integer again the program will accept it the second time. How do I make this program not accept the entry no matter how many times the user enters it?

        int[] shippedOrderNumbers = new int[5];

        Console.WriteLine("Please Input first Shipping Number: ");
        shippedOrderNumbers[0] = Convert.ToInt32(Console.ReadLine());           

        Console.WriteLine("Please Input second Shipping Number: ");
        shippedOrderNumbers[1] = Convert.ToInt32(Console.ReadLine());           


        if (shippedOrderNumbers[0] == shippedOrderNumbers[1])
        {
            Console.WriteLine("A dublicate number is not allowed please try again: ");
            shippedOrderNumbers[1] =Convert.ToInt32(Console.ReadLine());               
        }          

            Console.WriteLine("Please Input third Shipping Number: ");
            shippedOrderNumbers[2] = Convert.ToInt32(Console.ReadLine());


        if (shippedOrderNumbers[0] == shippedOrderNumbers[2] || shippedOrderNumbers[1] == shippedOrderNumbers[2])
        {
            Console.WriteLine("A dublicate number is not allowed please try again: ");
            shippedOrderNumbers[2] = Convert.ToInt32(Console.ReadLine());
        }                           
            Console.WriteLine("Please Input fourth Shipping Number: ");
            shippedOrderNumbers[3] = onvert.ToInt32(Console.ReadLine());               


        if (shippedOrderNumbers[0] == shippedOrderNumbers[3] || shippedOrderNumbers[1] == shippedOrderNumbers[3] || shippedOrderNumbers[2] == shippedOrderNumbers[3])
        {
            Console.WriteLine("A dublicate number is not allowed please try again: ");
            shippedOrderNumbers[3] = Convert.ToInt32(Console.ReadLine());
        }                           
            Console.WriteLine("Please Input fifth Shipping Number: ");
            shippedOrderNumbers[4] = Convert.ToInt32(Console.ReadLine());


        if (shippedOrderNumbers[0] == shippedOrderNumbers[4] || shippedOrderNumbers[1] == shippedOrderNumbers[4] || shippedOrderNumbers[2] == shippedOrderNumbers[4] || shippedOrderNumbers[3] == shippedOrderNumbers[4])
        {
            Console.WriteLine("A dublicate number is not allowed please try again: ");
            shippedOrderNumbers[4] = Convert.ToInt32(Console.ReadLine());
        }           

Answer 1

I think you would be better using a generic list rather than an array. You can also simplify you code by using a simple loop. Refer to the following for an example.

IList<int> shippedOrderNumbers = new List<int>();

for (int = 0; i < 5; i++)
{
    Console.WriteLine("Please input the Shipping Number: ");

    int shippingNumber;
    if (!Int.TryParse(Console.ReadLine(), out shippingNumber) 
    {
        Console.WriteLine("Your shipping number is not an integer");
    }

    if (shippedOrderNumbers.Contains(shippingNumber)) 
    {
        Console.WriteLine("This shipping number has already been entered.");
    }
    else 
    {
        shippedOrderNumbers.Add(shippingNumber);
        Console.WriteLine("Thanks for submitting your shipping number.");
    }
}

PS. I wrote this in notepad so it might not work but should give you a general guide on how to fix your issue.