Error in connection database

Once I run the program it give me this error:
An unhandled exception of type 'System.Data.OleDb.OleDbException' occurred in system.data.dll

Here is the code:
OleDbConnection Conn=new OleDbConnection(ConnString);
Conn.Open();
OleDbDataReader dr;
OleDbCommand dbcom=new OleDbCommand();
DataSet ds=new DataSet();
OleDbDataAdapter da=new OleDbDataAdapter();
da.SelectCommand=new OleDbCommand(Sqlstring,Conn);
da.Fill(ds);
dbcom.Connection=(Conn);
dbcom.CommandText=Sqlstring;
dr=dbcom.ExecuteReader();

it say the dbcom is undefined value.
How to fix it
Help!Thank Q

 

So,what should I do and how to fix it.
Thank Q

 

May I know how to correct it please?

 

Here is the whole program code

 

Sorry, because I don't know how to find the query as you know I'm the beginner of programming.If I did something please correct me!

 

it say the dbcom is undefined value.

 

If I don't going through the OleDb code. The data will not list at the list box there.

 

lieweffect probably you need to concentrate on basics first and get the grasp and then go for database programming in C#.

 

Thank Q for your advise coderzone
Actually the original program is in vb code.
It can run properly.
After I convert it into c# follow the c# syntax it cannot run.
So,may I know which is the mistake from the code
Thank Q

 

Thank Q
I try to create again