Randam Number Concatenate two string with insert the data in table

Create a table it has two column one is int type and another is varchar


string randomnumber()
{
SqlDataAdapter adp = new SqlDataAdapter("Select max(empid) as empid from emp1 ", con);
DataSet ds = new DataSet();
adp.Fill(ds);
string i="";
if (ds.Tables[0].Rows.Count > 0)
{
i = ds.Tables[0].Rows[0]["empid"].ToString();
}
if (i == "")
{
i = "0";
}
//i=i.Remove(0, 3);
i = (int.Parse(i) + 1).ToString();
if (i.Length == 2)
{
i = "OCG0" + i;
}
else if (i.Length == 1)
{
i = "OCG00" + i;
}
else if (i.Length > 2)
{
i = "OCG" + i;
}
return i;
}


int randomnumber1()
{
SqlDataAdapter adp = new SqlDataAdapter("Select max(empid) as empid from emp1 ", con);
DataSet ds = new DataSet();
adp.Fill(ds);
int i = 0;
if (ds.Tables[0].Rows.Count > 0)
{
i = Convert.ToInt32( ds.Tables[0].Rows[0]["empid"].ToString());
}
if (i.ToString() == "")
{
i = 0;
}

i = i + 1;

return i;
}

protected void Page_Load(object sender, EventArgs e)
{

if (!IsPostBack)
{

}
}
protected void btns_Click(object sender, EventArgs e)
{
SqlCommand com = new SqlCommand();
ListBox1.Items.Add(randomnumber().ToString());
con.Open();
com.CommandText = "insert into emp1 (empid,EMPCODE) values ("+randomnumber1()+" ,'" + randomnumber().ToString() +"')";
com.Connection = con;
com.ExecuteNonQuery();
con.Close();

}