bool allChecked;
if (l1tag == 1) allChecked = ...;
else if (l2tag == 2) allChecked = ...;
// continued...
if (allChecked)
{
rannum = randNum.Next(101);
textBox1 = rannum.ToString();
i++;
}
else
{
textBox1.Text = "Not Eligible for Roll";
i++;
}?
Edit: Frank has a way better solution, it depends how seriously you want to take the architecture.