Generate Random Number22

namespace RandomNoGenerate2
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }

        int min, max, val = 0;
        Random rdm;
        bool b;
        private void Form2_Load(object sender, EventArgs e)
        {
            for (int i = 1; i <= 30; i++)
            {
                comboBox1.Items.Add(i);
            }

            randomnoforcombo5();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            rdm = new Random();
            min = Convert.ToInt32(txt_min.Text);
            max = Convert.ToInt32(txt_max.Text);
            val = rdm.Next(min, max);
            comboBox1.Text = val.ToString();
        }

        private void link_Check_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
        {
            for (int i = 0; i < listBox2.Items.Count; i++)
            {
                if (comboBox2.Text == listBox2.Items[i].ToString())
                {
                    comboBox2.BackColor = Color.Tomato;
                    return;
                }                
            }
            listBox2.Items.Add(comboBox2.Text);
            comboBox2.BackColor = Color.White;
        }

        private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
        {
            for (int i = 0; i < listBox3.Items.Count; i++)
            {
                if (comboBox3.Text == listBox3.Items[i].ToString())
                {
                    comboBox3.BackColor = Color.Tomato;
                    return;
                }
            }
            listBox3.Items.Add(comboBox3.Text);
            comboBox3.BackColor = Color.White;
        }

        private void comboBox4_SelectedIndexChanged(object sender, EventArgs e)
        {            
            listBox4.Items.Add(comboBox4.Text);
            comboBox4.Items.Remove(comboBox4.Text);            
        }

        private void linkLabel5_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
        {
            Form2_Load(sender, e);
        }
        private void randomnoforcombo5()
        {
            rdm = new Random();
            min = Convert.ToInt32(txt_min.Text);
            max = Convert.ToInt32(txt_max.Text);
            val = rdm.Next(min, max);
            comboBox5.Text = val.ToString();
        }
    }
}