Login code using C# windows forms application

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

namespace First_Csharp_app
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
try
{
if (!(usertxt.Text == string.Empty))
{
if (!(passtxt.Text == string.Empty))
{
String str = "server=MUNESH-PC;database=windowapp;UID=sa;password=123";
String query = "select * from data where username = '" + usertxt.Text + "'and password = '" + this.passtxt.Text + "'";
SqlConnection con = new SqlConnection(str);
SqlCommand cmd = new SqlCommand(query, con);
SqlDataReader dbr;
con.Open();
dbr = cmd.ExecuteReader();
int count = 0;
while (dbr.Read())
{
count = count + 1;
}
if (count == 1)
{
MessageBox.Show("username and password is correct");
}
else if (count > 1)
{
MessageBox.Show("Duplicate username and password", "login page");
}
else
{
MessageBox.Show(" username and password incorrect", "login page");
}
}
else
{
MessageBox.Show(" password empty", "login page");
}
}

else
{
MessageBox.Show(" username empty", "login page");
}
// con.Close();

}
catch (Exception es)
{
MessageBox.Show(es.Message);

}
}
}
}

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