cannot implicitly convert type 'string' to 'int' in c#

Question

cannot implicitly convert type 'string' to 'int' in c# Windows Application

 

private int billno(string p)

{

string Billno = "0";

cmd = new SqlCommand(p, con);

con.Open();

SqlDataReader reader = cmd.ExecuteReader();

if (reader.Read())

{

Billno = reader[0].ToString();

}

reader.Close();

return Billno;

con.Close();

}

 

private void btn_Insert_Click(object sender, EventArgs e)

{

int Billno = billno("Select ISNULL(Max(Billno+1),1) From MainBillForm");

}