Random rnd = new Random();
            int val;
            string outstr = "";
            for (int i = 0; i < 7; ++i)
            {
                val = rnd.Next(0, 62);
                if (val < 26)
                    outstr += (char)(val + 'a');
                else if (val < 52)
                    outstr += (char)('A' + (val - 26));
                else
                {
                    outstr += (char)('0' + (val - 52));
                }
            }
            label1.Text = outstr.Trim();

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

namespace ConsoleApplication1
{
    class Program
    {
        static List<Char> randomNumbers(Int32 totalNumbers)
        {
            // create a new instance of random (default seed)
            Random rand = new Random();

            // create a new list of characters
            List<Char> outputList = new List<Char>();

            // keep adding random characters to list
            for (Int32 index = 0; index < totalNumbers; index++)
            {

                // random result is 1 add letter, else number
                if(rand.Next(0,2) == 1)
                {
                    // add a letter (ASCII 65-90 = A-Z)
                    outputList.Add((Char)rand.Next(65,90));
                }
                else
                {
                    // add a number (ASCII 48-50 = 0-9)
                    outputList.Add((Char)rand.Next(48, 57));
                }
            }

            // return list of random characters
            return outputList;
        }

        static void Main(string[] args)
        {
            foreach(Char element in randomNumbers(10))
            {
                Console.WriteLine(element);
            }
            Console.ReadKey();
        }
    }
}