I have a problem in this code .please

This is a bit off-topic, but why are you using the data adapter at all. As far as the code is shown, you create a command, set the parameters and execute the command. Adapter isn't necessary for this. So if you simply need to insert a row from few text boxes and you don't use any other adapter functionality in your code, you could possibly simplify this to:

con = new SqlConnection(dbconnection.constring);
SqlCommand cmd = new SqlCommand("INSERT INTO item VALUES (@item_name,@price)", con);
cmd.Parameters.Add("@item_name", SqlDbType.NVarChar).Value = textBox1.Text;
cmd.Parameters.Add("@price", SqlDbType.Money).Value = textBox2.Text;
con.Open();
cmd.ExecuteNonQuery();
con.Close();

Below code worked for me .

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;   
using System.Data.SqlClient;
using System.Data.SqlTypes;
using System.Data.Sql;


namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {

            SqlConnection con = new SqlConnection("user id=dbuser;" +
                                       "password=pass@123;server=10.1.2.21;" +
                                       "Trusted_Connection=yes;" +
                                       "database=TestDB; " +
                                       "connection timeout=30");          
            SqlCommand cmd = new SqlCommand("INSERT INTO item VALUES (@item_name,@price)", con);
            cmd.Parameters.Add("@item_name", SqlDbType.NVarChar).Value = '1';
            cmd.Parameters.Add("@price", SqlDbType.Money).Value = 100;
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();

        }
    }
}