Add Items to List Randomly

Question

I am fetching 50 questions from Api https://supaquizapi.azurewebsites.net/api/Questions

Loading into list and deleting 40 questions randomly.

Now I just to add 10 questions randomly to Questions

  List<InQuestion> res = await GetApiData();
            Questions.AddRange(res.Select(r => new Question
            {
                SNo = r.No,
                Topic = r.Topic,
                QuestionTitle = r.QuestionTitle,
                Options = new List<string>() { r.Opt1, r.Opt2, r.Opt3, r.Opt4 },
                Answer = r.Answer,
                Time = r.Time,
                Correct = r.Correct,
                Solution = r.Solution
            }));
            int maxnumber = (from e in Questions select e.SNo).Max();
            int minumber = (from e in Questions select e.SNo).Min();
            int range = maxnumber + 1;
            string stopflag = "Y";
            while (stopflag == "Y")
            {
                Random rand = new Random();
                int ranumber = rand.Next(0, range);
                var result = Questions.FirstOrDefault(c => c.SNo == ranumber);
                if (result != null)
                { Questions.Remove(result); }
                int count = (from e in Questions select e.SNo).Count();
                if (count == 10)
                { stopflag = "N"; }
            }

Answer 1

To keep 10 questions only, try this:

Random rand = new Random();

while( Questions.Count > 10 ) 
{
    Questions.RemoveAt(rand.Next( Questions.Count ) );
}

Answer 2

I added where clause

 List<InQuestion> res = await GetApiData();
            List<InQuestion> dest;
               string stopflag = "Y";
            int maxnumber = (from e in res select e.No).Max();
            int minumber = (from e in res select e.No).Min();
            int range = maxnumber + 1;
            Random rand = new Random();
            int ranumber;
            while (stopflag == "Y")
            {
                 ranumber = rand.Next(0, range);
                var result = Questions.FirstOrDefault(c => c.SNo == ranumber);
            //   dest= res.FirstOrDefault(c => c.No == ranumber);
                if (result == null)
            {
                Questions.AddRange(res.Where(r => r.No == ranumber).Select(r => new Question
                {
                    SNo = r.No,
                    Topic = r.Topic,
                    QuestionTitle = r.QuestionTitle,
                    Options = new List<string>() { r.Opt1, r.Opt2, r.Opt3, r.Opt4 },
                    Answer = r.Answer,
                    Time = r.Time,
                    Correct = r.Correct,
                    Solution = r.Solution
                }));
                }
                int count = (from e in Questions select e.SNo).Count();
                if (count == 10)
                { stopflag = "N"; }
            }
            /*