生成不包括特定范围值的随机数 - C#

Question

I have 4 batches:

10000-30000
30001-50000
50001-70000
71000-99999

I have to generate 500 random numbers for the followings groups excluding the values from {70000-71000}

My code is somewhat like this. My datagrid shows 500 records but it has numbers between {70-71k}.I need to calculate the count which is not giving me the required "500" count because certain random numbers are getting generated between {70-71k} which i need to exclude.

   int i=10000, j=99999;
    int batch1Count = 0, batch2Count = 0, batch3Count = 0, batch4Count = 0;
    private void button1_Click(object sender, EventArgs e)
    {
        try
        {
            this.dataGridView1.Rows.Clear();

            string prefix = comboBox1.SelectedValue.ToString();
            switch (prefix)
            {
                case "1": prefix = "USN"; break;
                case "2": prefix = "DOT"; break;
                case "3": prefix = "USAF"; break;
                case "4": prefix = "COV"; break;
            }

            for (int k = 0; k < 500; k++)
            {

                Random random = new Random(DateTime.UtcNow.Millisecond);
                //Generate random values                   
                int result = random.Next(i,j);
                Thread.Sleep(1);
                if (result >= 70000 && result <= 71000)
                {
                    k=k-1;
                }
                else
                {
                    //Add prefix to the generated random value
                    string key = prefix + result;

                    DataGridViewRow row = new DataGridViewRow();
                    row.CreateCells(dataGridView1);
                    row.Cells[0].Value = key;
                    this.dataGridView1.Rows.Add(row);

                    Thread.Sleep(3);
                    if (result >= 10000 && result <= 30000)
                    {
                        Thread.Sleep(1);
                        batch1Count++;

                    }
                    else if (result >= 30000 && result <= 50000)
                    {
                        Thread.Sleep(1);
                        batch2Count++;
                    }
                    else if (result >= 50000 && result <= 70000)
                    {
                        Thread.Sleep(1);
                        batch3Count++;
                    }
                    else if (result >= 71000 && result <= 99999)
                    {
                        Thread.Sleep(1);
                        batch4Count++;
                    }
                }
            }
        }
        catch (Exception ex)
        { }
    }

Answer 1

Can't you just use the Random class for it?

The Random class has a Next(int, int) method that generates a random number between the specified values. You could simply generate one and if it is in the {70k-71k} range, generate another one.

Answer 2

Rather than throwing out numbers that are in the range 70000-71000, generate a number from 10000-89999 and if it's greater than 70000 then add 1000 to it. For example:

var num = rnd.Next(10000, 90000);
if (num > 70000)
{
    num += 1000;
}

You're just mapping the numbers in the range 70001-89999 to 71001-99999.