using System;

public class Program

{

    public static void Main()

    {

        var chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz";

        var stringLength = 10;  

        var randomString = "";     

        var rand = new Random();

        for(var x = 0; x < stringLength; x++) {

            var letterOrNumber = rand.Next(0,2);

            //Console.WriteLine(letterOrNumber);  

            if(letterOrNumber == 0){

                var newNum = rand.Next(0,10);

                randomString += newNum;

            } 

            else {

                var rnum = rand.Next(0, chars.Length);

                randomString += chars.Substring(rnum,1);

            }

        }

        Console.WriteLine(randomString);

    }   

}