C# and SQL project exe to forms and codes

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
using System.Configuration;

namespace Server
{
    class Class1
    {

        string constring = Convert.ToString(ConfigurationSettings.AppSettings["ConnectionString"]);
        SqlCommand cmd1, cmd2, c, c1, cmd3,cmd7;
        string id, id1, id2, id3, id4;
        int eid, eid1, eid2, eid3, eid4;

        public int idgeneration()
        {
            SqlConnection con = new SqlConnection(constring);
            con.Open();
            SqlCommand c1;
            c1 = new SqlCommand("select max(ID) from Registration", con);
            id = Convert.ToString(c1.ExecuteScalar());
            if (id == "")
            {
                eid = 1;
            }
            else
            {
                eid = Convert.ToInt16(id);
                eid = eid + 1;
            }
            con.Close();
            return eid;
        }

        public int uploadfileid()
        {
            SqlConnection con1 = new SqlConnection(constring);
            con1.Open();
            SqlCommand c1;
            c1 = new SqlCommand("select max(fileid) from uploadfiles", con1);
            id1 = Convert.ToString(c1.ExecuteScalar());
            if (id1 == "")
            {
                eid1 = 1;
            }
            else
            {
                eid1 = Convert.ToInt16(id1);
                eid1 = eid1 + 1;
            }
            con1.Close();
            return eid1;
        }



        public int senditems()
        {
            SqlConnection con1 = new SqlConnection(constring);
            con1.Open();
            SqlCommand c1;
            c1 = new SqlCommand("select max(Req_ID) from senditems", con1);
            id1 = Convert.ToString(c1.ExecuteScalar());
            if (id1 == "")
            {
                eid1 = 1;
            }
            else
            {
                eid1 = Convert.ToInt16(id1);
                eid1 = eid1 + 1;
            }
            con1.Close();
            return eid1;
        }



        public int autoid()
        {
            SqlConnection con4 = new SqlConnection(constring);
            con4.Open();
            SqlCommand c5;
            c5 = new SqlCommand("select max(autid) from usersearch", con4);
            id2 = Convert.ToString(c5.ExecuteScalar());
            if (id2 == "")
            {
                eid2 = 1;
            }
            else
            {
                eid2 = Convert.ToInt16(id2);
                eid2 = eid2 + 1;
            }
            con4.Close();
            return eid2;
        }
        public void uploadfile(string fid, string finame, byte[] File, string time, string path1,string ext)
        {

            SqlConnection con2 = new SqlConnection(constring);
            con2.Open();
            int n = finame.Length;
            cmd2 = new SqlCommand("insert into uploadfiles values('" + fid + "','" + finame + "',@File,'" + time + "','" + path1 + "','"+ext+"')", con2);
            cmd2.Parameters.AddWithValue("@File", File);
            cmd2.ExecuteNonQuery();
            con2.Close();
        }





        public void senditems(string reqid, string sendid, string fname, byte[] File, string uname, string userip, string send)
        {

            SqlConnection con7 = new SqlConnection(constring);
            con7.Open();
            int n = fname.Length;
            cmd7 = new SqlCommand("insert into senditems values('" + reqid + "','" + sendid + "','" + fname + "',@File,'" + uname + "','" + userip + "','"+send+"')", con7);
            cmd7.Parameters.AddWithValue("@File", File);
            cmd7.ExecuteNonQuery();
            con7.Close();
        }



       
        public void usersearch(string auid, string reqid, string usrid, string unam, string filnm, string dat, string sta)
        {
            SqlConnection con3 = new SqlConnection(constring);
            con3.Open();
            cmd3 = new SqlCommand("insert into usersearch values('" + auid + "','" + reqid + "','" + usrid + "','" + unam + "','" + filnm + "','" + dat + "','Key not send')", con3);
            cmd3.ExecuteNonQuery();
            con3.Close();
        }
        public void keymaintain(string aid, string reqid, string usrid, string secretky, string path, string path1)
        {
            SqlConnection con4 = new SqlConnection(constring);
            con4.Open();
            cmd1 = new SqlCommand("insert into keymaintenance values('" + aid + "','" + reqid + "','" + usrid + "','" + secretky + "','" + path + "','')", con4);
            cmd1.ExecuteNonQuery();
            con4.Close();
        }


    }

}

problem on connecting string so please help me how to connect