I am unable to count rows from my database table.

Better you follw this

//Connecion string .....
            SqlCommand cmd= new SqlCommand("select count(*) from test", con);
	    int noRows;
            con.Open();
	    noRows = cmd.ExecuteNonQuery();
	    con.Close();
	    label1.Text= Convert.ToString(noRows);

Hi,

You did not initiate your connection or command object.

Thanks...

Your code looks fine
Please check your connection and command objects whatever you defined outside.

See it's instantiating or not

private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                con.Open();
                cmd.CommandText = "select count(*) from test;";
                cmd.Connection = con;
                int a = (int)cmd.ExecuteScalar();  
                con.Close();     
                label1.Text = a.ToString();
            }
            catch (Exception err)
            {
                MessageBox.Show(err.Message);
                this.Close();
            }
        }

You have to create instance of your sqlconnection and sqlcommand with new operator.
No need to write dr.Close();

Please try this way. It works.

try
 {
     string connectionString = "Your connection string";
     SqlConnection con = new SqlConnection(connectionString);
     SqlCommand cmd = new SqlCommand();
     con.Open();
     cmd.CommandText = "select count(*) from test;";
     cmd.Connection = con;
     int a = (int)cmd.ExecuteScalar();
     con.Close();
     string status = Convert.ToString(a);
    // label1.Text = status;
 }
 catch (Exception err)
 {
     MessageBox.Show(err.Message);
     this.Close();
 }