using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.OleDb;

namespace ConsoleApplication1
{
    class ExcelReader
    {
        OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Documents and Settings\user\My Documents\test.xls;Extended Properties=Excel 8.0");
        OleDbCommand com  = new OleDbDataAdapter("select * from table", con);
        con.Open(); //Error is here
    }
}

using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.OleDb;

namespace ConsoleApplication1
{
    class ExcelReader
    {
        OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Documents and Settings\jcafaro\My Documents\test.xls;Extended Properties=Excel 8.0");
        OleDbCommand com  = new OleDbCommand("select * from table", con);
        con.Open();
    }
}

insert into table1 values (1,2,3,4)

insert into table1 (A,B,C,D) values (1,2,3,4)

insert into table1 values ("hi",2,3,4)

insert into table1 values (hi,2,3,4)

Enter Command: insert into table1 values (\"hi\",2,3,4)
Invalid Command: Syntax error (missing operator) in query expression '\"hi\"'.
Enter Command: insert into table1 values (\'hi\',2,3,4)
Invalid Command: Syntax error (missing operator) in query expression '\'hi\''.
Enter Command: insert into table1 values ('hi',2,3,4)
Invalid Command: Data type mismatch in criteria expression.
Enter Command: insert into table1 values ("hi",2,3,4)
Invalid Command: Data type mismatch in criteria expression.

static String EnterCommand()
        {
            Console.Write("Enter Command: ");
            String result = Console.ReadLine();
            if (result.Equals("q"))
                return result;
            else if (result.Equals("c"))
            {
                ShowColumns(dt);
                return "";
            }
            else
            {
                OleDbCommand com = new OleDbCommand(result, con);   //Prepares the command
                dat.SelectCommand = com;    // Links the table to the command
                try
                {
                    dt.Clear(); // Clear the temporary table
                    dat.Fill(dt); // "Fill" up the temporary table with whatever is in dat as a result of the command
                    ShowResults(dt);
                }
                catch (Exception e)
                {
                    Console.WriteLine("Invalid Command: " + e.Message);
                }
                return "";
            }
        }