❔ Random Letter

using System;
using System.IO;

class GFG{

public static void Main(string[] args)
{
    Random res = new Random();

    String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

    String randomstring = "";
    for (int i = 0; i < 1000; i++){
        for (int a = 0; a < 7; a++)
        {

          int x = res.Next(str.Length);
          randomstring = randomstring + str[x];
        }
        string file = @"codes.txt";
        File.WriteAllText(file, $"{randomstring}\n");
        Console.WriteLine("Random alphanumeric String:" + randomstring);
    }

}
}