How Create Sequence number in Controller action? - asp.net-mvc

Question

I am working on a project which is an E-health patient Gateway.
I want to generate a number (int type) against a submit form from View to Controller (When phlebotomist receives the blood sample he will check the box and click on submit button). This number is the patient's blood sample number that will be generated in my controller and will be saved in the database. I am using the logic below to create the number but it always gives me zero.
Kindly let me know how I can create numbers one by one in sequence and store in database?
public ActionResult AddSampleTest(int Pid, int Tid, int Stid, string Comment ,string testDate,int DotorID)
{
int sampleNumber=1;
Random rnd = new Random();
int[] sample = new int[50000];
rnd.Next();
for (int ctr = 1; ctr <= sample.Length; ctr++)
{
sampleNumber=sample[ctr + 1];
}
string sampleno = sampleNumber.ToString();
DateTime TestDate = Convert.ToDateTime(testDate);
int Recomended_Test_DoctorID = DotorID;
// Update the Sample Status
PatientTest objpatientTest = db.PatientTests.Where(x => x.PatientID == Pid && x.Testid == Tid && x.SubTestId == Stid && x.Date==TestDate &&x.DoctorId== Recomended_Test_DoctorID).FirstOrDefault();
objpatientTest.SampleStatus = "Sample Received";
objpatientTest.SampleNumber = sampleno;
db.SaveChanges();
var name = User.Identity.Name;
int Lid = db.LabAttendantRecords.Where(x => x.Name == name).Select(x => x.User_id).FirstOrDefault();
LabTestSample obj = new LabTestSample();
obj.labtestid = Tid;
obj.PatientId = Pid;
obj.subtestid = Stid;
obj.labAtendid = Lid;
obj.date = DateTime.Now.Date;
obj.sampleReceived = true;
obj.Comment = sampleno;
db.LabTestSamples.Add(obj);
db.SaveChanges();
return RedirectToAction("TestSampleNumber", "LabAttendantDashboard", new { sampleno});
// Use This for add Result
return RedirectToAction("SubTest", "LabAttendantDashboard", new { Pid, Tid, Stid });
}

Answer 1

sampleNumber is always 0 because each element in sample is 0.
If you want it to be a random number you need to do something like :
Random rnd = new Random();
int sampleNumber = rnd.Next();
string sampleno = sampleNumber.ToString();
If you need to be sure that the sample number is unique, you should use a Guid :
string sampleno = Guid.NewGuid().ToString();