Diffrent digits

I'm glad that one of us was awake, yesterday, Roy ;)

How I missed that I don't know!

Matan did start a separate thread where he asked for a solution to this using both integers and doubles but it then got mysteriously deleted.

Anyway, doubles are tricky given that they usually have an approximate representation within the machine. Consequently, when you start multiplying or dividing by 10, some of the lower order digits can change and mess up the program. The best solution I've been able to come up with is to convert the double to decimal which crystallizes the initial digits and after that arithmetic is exact:

using System;
using System.Numeric;

class Program
{
    static void Main()
    {
        bool[] used = new bool[10]; // all false by default
        Console.Write("Enter a number : ");
        double number = double.Parse(Console.ReadLine());
        decimal num = (decimal)Math.Abs(number); // convert to decimal and ignore sign
        bool different = true;

        while (num != Decimal.Truncate(num)) num *= 10m; // move all digits to right of dp to left of dp
   
        Console.WriteLine("The digits are\n");

        while (num > 0m)
        {
            int digit = (int)(num % 10m);
            num /= 10m;
            num = Decimal.Truncate(num);
            Console.WriteLine(digit); // print out digits so we can see what's happening
            if (used[digit])
            {
                different = false;
                break;
            }
            else
            {
                used[digit] = true;
            }
        }

        Console.WriteLine();

        if (different)
        {
            Console.WriteLine("Digits are different");
        }
        else
        {
            Console.WriteLine("Digits are not different");
        }
        Console.ReadKey();
    }
}

It is possible without strings (however, I don't really get why you don't want to use them).

I just changed Vulpes code a bit. The digits are now obtained by dividing the number by 10 and taking the rest of that division as the digit.

EDIT: Realised it was a bit silly to actually store the digits in a list/array...

using System;

class Program
{
    static void Main()
    {
        bool[] used = new bool[10]; // all false by default
        Console.Write("Enter a number : ");
        int number = int.Parse(Console.ReadLine());
        bool different = true;

        while (number > 0)
        {
            int digit = number % 10;
            number /= 10;

            if (used[digit])
            {
                different = false;
                break;
            }
            else
            {
                used[digit] = true;
            }
        }

        if (different)
        {
            Console.WriteLine("Digits are different");
        }
        else
        {
            Console.WriteLine("Digits are not different");
        }
        Console.ReadKey();
    }
}

I need an algorithm.

BTW, perhaps the easiest of all ways to do this is to use LINQ (VS 2008 or later). However, string processing is still being used under the hood:

Unless there's some clever algorithm, I can't think of a way of doing it without considering the individual digits in the string.

Do you have anything in mind?

Here's a more traditional way of doing it, if you're still using VS 2005 or don't want to use HashSet for some reason:

An easy way to do it is to read the numeric string entered into a HashSet which automatically excludes duplicates. If the number of elements in the HashSet is the same as the original number string, then the digits must be different.

Here's a quick example of this technique (needs VS 2008 or later):

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
       Console.Write("Enter a number : ");
       string number = Console.ReadLine();
       HashSet hs = new HashSet(number); // automatically removes duplicates
       if (hs.Count == number.Length)
       {
          Console.WriteLine("Digits are different");
       }
       else
       {
          Console.WriteLine("Digits are not different");
       }
       Console.ReadKey();  
    }
}