c# problem kod querija

Code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Data.OleDb;
using System.Windows.Forms;

namespace zadatak2
{
    public partial class Form1 : Form
    {
        private OleDbConnection connection=new OleDbConnection();
        public Form1()
        {
            connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\VS2010 projects\zadatak2\zadatak2\fedek.accdb;Jet OLEDB:Database Password=fedek;";
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            try
            {

                connection.Open();
                OleDbCommand command=new OleDbCommand();
                command.Connection=connection;
                string query="select * from konf";
                command.CommandText=query;
                
                OleDbDataReader reader=command.ExecuteReader();
                while(reader.Read())
                {
                    comboBox1.Items.Add(reader["korisnik"].ToString());
                    comboBox2.Items.Add(reader["dogadjaj"].ToString());
            }
               
            }
            catch(Exception ex)
            {
                MessageBox.Show("error" + ex);
            }

            connection.Close();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            string query = "insert into Tomislav (Korisnik, Dogadjaj, DatumOd, DatumDo) values('" + this.comboBox1.SelectedItem + "','" + this.comboBox2.SelectedItem + "''" + this.dtpOd.Text + "''" + this.dtpDo.Text + "') ;";

           
          

            OleDbCommand command1 = new OleDbCommand();
            command1.Connection = connection;
            command1.CommandText = query;

            OleDbDataReader reader;


            try
            {
                connection.Open();

                reader = command1.ExecuteReader();
                MessageBox.Show("saved");
                while (reader.Read())
                {
                }

            }

            catch (Exception ex1)
            {
                MessageBox.Show("error" + ex1);
            }

            connection.Close();
        }

       

       

       
    }
}

Code:
this.comboBox2.SelectedItem + "''" + this.dtpOd.Text + "''" + this.dtpDo.Text + "') ;";

Code:

this.dtpOd.Text

Code:

this.dtpOd.Value.ToString("format koji razume access")

Code:


string query = "insert into Tomislav (Korisnik, Dogadjaj, DatumOd, DatumDo) values('" + this.comboBox1.SelectedItem + "','" + this.comboBox2.SelectedItem + "','" + this.dtpOd.Value.Date + "','" + this.dtpDo.Value.Date + "') ;";

Code:
http://speedy.sh/mVqGn/fedek.accdb

Code:

private void button1_Click(object sender, EventArgs e)
        {
            Random random = new Random();
            int newSelectedIndex = comboBox1.SelectedIndex;
            while (newSelectedIndex == comboBox1.SelectedIndex)
            {
                newSelectedIndex = random.Next(0, comboBox1.Items.Count);
            }
            comboBox1.SelectedIndex = newSelectedIndex;
        }

Code:

        private void button1_Click(object sender, EventArgs e)
        {
            Random r = new Random((int)DateTime.Now.Ticks);

            cbKorisnici.SelectedIndex = r.Next(0, cbKorisnici.Items.Count);
            cbDogadjaji.SelectedIndex = r.Next(0, cbDogadjaji.Items.Count);

            Save();
        }

Code:

dtpOd.Format = DateTimePickerFormat.Custom;
dtpOd.CustomFormat = "ddddd, MMMM dd, yyyy hh:mm:ss tt"; 

Code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Data.OleDb;
using System.Windows.Forms;

namespace zadatak2
{
    public partial class Form1 : Form
    {
        private OleDbConnection connection=new OleDbConnection();
        public Form1()
        {
            connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\VS2010 projects\zadatak2\zadatak2\fedek.accdb;Jet OLEDB:Database Password=fedek;";
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            dtpOd.Format = DateTimePickerFormat.Custom;
            dtpOd.CustomFormat = "ddddd, MMMM dd, yyyy hh:mm:ss tt";
            dtpDo.Format = DateTimePickerFormat.Custom;
            dtpDo.CustomFormat = "ddddd, MMMM dd, yyyy hh:mm:ss tt"; 

                connection.Open();
                
                string query="SELECT korisnik from korisnici";
                string query2 = "select dogadjaj from dogadjaji";
                OleDbCommand command = new OleDbCommand(query, connection);
                command.Connection = connection;
                OleDbDataReader reader = command.ExecuteReader();

               
                
             
                while(reader.Read())
                {

                    comboBox1.Items.Add(reader["korisnik"].ToString());
                   
                    
            }
                command = new OleDbCommand(query2, connection);
                reader = command.ExecuteReader();
                while (reader.Read())
                {
                    comboBox2.Items.Add(reader["dogadjaj"].ToString());
                }
           
           

            connection.Close();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
          
            string query = "insert into Tomislav (Korisnik, Dogadjaj, DatumOd, DatumDo) values('" + this.comboBox1.SelectedItem + "','" + this.comboBox2.SelectedItem + "','" + this.dtpOd.Value.Date + "','" + this.dtpDo.Value.Date + "') ;";
           
          

            OleDbCommand command1 = new OleDbCommand();
            command1.Connection = connection;
            command1.CommandText = query;

            OleDbDataReader reader;


            try
            {
                connection.Open();

                reader = command1.ExecuteReader();
                MessageBox.Show("Saved");
                while (reader.Read())
                {
                }

            }

            catch (Exception ex1)
            {
                MessageBox.Show("error" + ex1);
            }

            connection.Close();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            new Random((int)DateTime.Now.Ticks);  
                int staro1 = comboBox1.SelectedIndex;
                int staro2 = comboBox2.SelectedIndex;
     
                comboBox1.SelectedIndex = (new Random()).Next(comboBox1.Items.Count);
                comboBox2.SelectedIndex = (new Random()).Next(comboBox2.Items.Count);
     
                string tekstKomande = "insert into Tomislav (Korisnik, Dogadjaj, DatumOd, DatumDo) values('" + this.comboBox1.SelectedItem + "','" + this.comboBox2.SelectedItem + "','" + this.dtpOd.Value.Date + "','" + this.dtpDo.Value.Date + "') ;";
     
     
                OleDbCommand command1 = new OleDbCommand();
                command1.Connection = connection;
                command1.CommandText = tekstKomande;

                OleDbDataReader reader;


                try
                {
                    connection.Open();

                    reader = command1.ExecuteReader();
                    MessageBox.Show("saved");
                    while (reader.Read())
                    {
                    }

                }

                catch (Exception ex1)
                {
                    MessageBox.Show("error" + ex1);
                }

                connection.Close();
     
                comboBox1.SelectedIndex = staro1;
                comboBox2.SelectedIndex = staro2;
            }
        }

  

       

       

       
    }

Code:

if (dtDatumOd.Value.Ticks < dtDatumDo.Value.Ticks)
{
    byte[] buffer = new byte[sizeof(long)];

    _random.NextBytes(buffer);
    long value1 = (Math.Abs(BitConverter.ToInt64(buffer, 0)) % (dtDatumDo.Value.Ticks - dtDatumOd.Value.Ticks)) + dtDatumOd.Value.Ticks;

    _random.NextBytes(buffer);
    long value2 = (Math.Abs(BitConverter.ToInt64(buffer, 0)) % (dtDatumDo.Value.Ticks - dtDatumOd.Value.Ticks)) + dtDatumOd.Value.Ticks;

    DateTime datumOd = new DateTime(Math.Min(value1, value2));
    DateTime datumDo = new DateTime(Math.Max(value1, value2));
}

Code:

 private void button1_Click(object sender, EventArgs e)
        {
            int intTextBox;
            intTextBox = Convert.ToInt32(txtBroj.Text);
            intTextBox = int.Parse(txtBroj.Text);
            for (int i = 0; i < intTextBox + 1; i++)
            {
                int staro1 = comboBox1.SelectedIndex;
                int staro2 = comboBox2.SelectedIndex;

                comboBox1.SelectedIndex = (new Random()).Next(comboBox1.Items.Count);
                comboBox2.SelectedIndex = (new Random()).Next(comboBox2.Items.Count);
                if (dtpOd.Value.Ticks < dtpDo.Value.Ticks)
                {
                    byte[] buffer = new byte[sizeof(long)];

                    random.NextBytes(buffer);
                    long value1 = (Math.Abs(BitConverter.ToInt64(buffer, 0)) % (dtpDo.Value.Ticks - dtpOd.Value.Ticks)) + dtpOd.Value.Ticks;

                   random.NextBytes(buffer);
                    long value2 = (Math.Abs(BitConverter.ToInt64(buffer, 0)) % (dtpDo.Value.Ticks - dtpOd.Value.Ticks)) + dtpOd.Value.Ticks;

                    DateTime datumOd = new DateTime(Math.Min(value1, value2));
                    DateTime datumDo = new DateTime(Math.Max(value1, value2));
                }

                string tekstKomande = "insert into Tomislav (Korisnik, Dogadjaj, DatumOd, DatumDo) values('" + this.comboBox1.SelectedItem + "','" + this.comboBox2.SelectedItem + "','" + this.dtpOd.Value + "','" + this.dtpDo.Value + "') ;";

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