C# Login Page Windows Form Application - OleDbException Unhandled
<p>Previously tried creating a login page with just username and password.
However, since my user table has 3 roles, i would like to create a login page that grants login to the user based on their role. </p>

<p>Eg: Admin to admin page, Staff to staff page etc.</p>

<p>Faced the following error in one of my line while trying to implement this:
OleDbException was unhandled, No value given for one or more parameters.</p>

<p>Here is my login code: </p>

<pre><code>using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;

namespace AcuSapp
{
    public partial class Login : Form
    {
        OleDbConnection LoginLink = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\SB18\\Documents\\Visual Studio 2010\\Projects\\AcuSapp\\AcuSapp\\bin\\debug\\AcuzioSecureStore DatabaseX.accdb");
        public Login()
        {
            InitializeComponent();
            //textBox_username.Text = "LittleJohn";
            //textBox_password.Text = "HelloJohn";
        }


        private void button_login_Click(object sender, EventArgs e)
        {
             string username = textBox_username.Text;
            string password = textBox_password.Text;
            string role_name = comboBox_role.Text;

            //this is to give notification if username and password is lesser than 4 characters
            // .length will count the characters in the string
            // This is to reduce redundant calls. Less calls = less taxing on the db
            if ((username.Length &lt; 4) || (password.Length &lt; 4))
            {
                MessageBox.Show("Wrong Credentials!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            else
            {
                // Set authentication as false. By default, user is not authenticated yet.
                bool isAuthenticated = false;
                //Opens the connection to db
                LoginLink.Open();
                // Sets the SQL command to be executed
                // Since it is a variable command, it becomes a new SQL command to be executed in Microsoft access
                // + is to join the string together
                //Does string comparing to see if username and password match exactly, case sensitive.

                //var cmd = new OleDbCommand("SELECT COUNT(*) FROM [User] WHERE username = '" + username + "' AND password = '" + password + "' ", LoginLink);
                var cmd = new OleDbCommand("SELECT COUNT(*) FROM [User] WHERE STRCOMP(username, '" + username + "', 0) = 0 AND STRCOMP(password, '" + password + "', 0) = 0 AND STRCOMP(role_name, '" + role_name + "', 0) = 0", LoginLink);
                // (int)cmd.ExecuteScalar only reads the first few rows from the db
                isAuthenticated = (int)cmd.ExecuteScalar() == 1; //Error on this line.
                //Closes connection to db
                LoginLink.Close();
                // if isAuthenticated is true
                if (isAuthenticated)
                {
                    // This will open the next page which is form1
                    Client hello = new Client(this);
                    hello.Show();
                    // Hides the login form
                    this.Hide();
                }
                else
                {
                    //Always remember to put the last statement in curly braces
                    //otherwise it wont show the previous error will show this messsage instead
                    MessageBox.Show("Wrong Credentials!");
                }
            }


        }
    }
}
</code></pre>
