C# Simple console application displaying/logical issue

Question

        List<int> numberList = new List<int>();
        List<int> uniqueList = new List<int>();

        string input;
        int number = 0;
        bool over = false;

        while (!over)
        {
            input = Console.ReadLine();
            if (input == "quit")
            {
                over = true;
                break;
            }
            if (int.TryParse(input, out number))
            {
                numberList.Add(number);
            }
        }

        for (int i = 0; i < numberList.Count; i++)
        {
            if (!uniqueList.Contains(number))
            {
                uniqueList.Add(number);
            }
        }

        for (int i = 0; i < uniqueList.Count; i++)
        {
            Console.WriteLine(uniqueList[i]);
        }

        Console.ReadKey();

Hi! I need some help with this program that takes in numbers, but upon typing "quit", it should list all the unique numbers that have been entered.

For example here's the input: 5, 5, 5, 2, 2, 1, 3 The console should only display 1 and 3 because they are the only unique numbers.

The problem is, that the program in its current form only displays the last unique number that has been entered, not all of them and I don't know why.

Could you tell me why? What do I need to do to list all of them?

Answer 1

You need to use a Dictionary to record the count of each number, then return the unique ones:

    Dictionary<int, int> numberDictionary = new Dictionary<int, int>();

    string input;
    int number = 0;
    bool over = false;

    while (!over)
    {
        input = Console.ReadLine();
        if (input == "quit")
        {
            over = true;
            break;
        }
        if (int.TryParse(input, out number))
        {
            if (numberDictionary.TryGetValue(number), out int count)
            {
                numberDictionary[number] = count + 1;
            }
            else
            {
                numberDictionary.Add(number, 1);
            } 
        }
    }

    foreach(var item in numberDictionary)
    {
        if (item.Value == 1)
        Console.WriteLine(item.Key);
    }

    Console.ReadKey();

Answer 2

You can do this much simpler

List<int> numbers = new List<int>{1, 2, 2, 3, 3, 3, 4, 4, 4, 5, 6, 6, 6};
var unique = numbers.Where(n => numbers.Count(m => m == n) == 1);
foreach(var u in unique)
    WriteLine(u);

Prints

1

5

What this is doing is it is takign the List numbers, and it Where looks at each member in the list (in this case that member is called n).

It then checks if the number of occurences of n is equal to 1. If it is this must be unique.

So for the first number in our list 1, the following:

numbers.Count(m => m == n)

Will return 1.

When n is 2 then

numbers.Count(m => m == n)

Will return 2.

Answer 3

This is a full implementation of the solution :

using System;
using System.Collections.Generic;
using System.Linq;

namespace EntryPoint.Concole
{
    class Program
    {
        static void Main(string[] args)
        {
           List<int> numberList = new List<int>();
           List<int> uniqueList = new List<int>();

           string input;
           int number = 0;
           bool over = false;

           while (!over)
           {
               input = Console.ReadLine();
               if (input == "quit")
               {
                  over = true;
                  break;
               }
               if (int.TryParse(input, out number))
               {
                  numberList.Add(number);
               }
           }

           var numbersDistinct = numberList.GroupBy(i => i);

           foreach (var num in numbersDistinct)
           {
              if (num.Count() == 1)
              {
                  uniqueList.Add(num.Key);
              }
           }

           for (int i = 0; i < uniqueList.Count; i++)
           {
              Console.WriteLine(uniqueList[i]);
           }

           Console.ReadKey();
        }
    }

Answer 4

I have checked and fixed your code. Although it is not perfect but I have pointed out the crucial mistakes.

        List<int> numberList = new List<int>();
        List<int> uniqueList = new List<int>();

        string input;
        int number = 0;
        bool over = false;

        while (!over)
        {
            input = Console.ReadLine();
            if (input == "quit")
            {
                over = true;
                //break; // it is not needed since you have over = true
            }
            if (int.TryParse(input, out number))
            {
                numberList.Add(number);
            }
        }

        for (int i = 0; i < numberList.Count; i++)
        {
            //if (!uniqueList.Contains(number)) // this is the wrong line
            if (numberList.Count(q => q == numberList[i]) == 1)
            {
                //uniqueList.Add(number); // this is also wrong
                uniqueList.Add(numberList[i]);
            }
        }

        for (int i = 0; i < uniqueList.Count; i++)
        {
            Console.WriteLine(uniqueList[i]);
        }

        Console.ReadKey();

In simple words the Count(...) method in the

numberList.Count(q => q == numberList[i]) == 1

line just counts elements of the numberList which satisfy provided condition. In this case, condition is q == numberList[i] which basically means to count elements that equal to numberList[i].

You may also read about delegates and lambda expressions in C# for better understanding.