public partial class FrmNewUser : System.Web.UI.Page
{
    SqlConnection conn = new SqlConnection("Data Source=SONIA-B408A4159\\SQLEXPRESS;Initial catalog=sonia;Integrated Security=true");
    string query;
    SqlCommand cmd;
 
    public string name="Code";
 
    protected void Page_Load(object sender, EventArgs e)
    {
              btnRegister.Attributes.Add("onclick", "javascript:return LenofPassword()");
    }
    protected void btnRegister_Click(object sender, EventArgs e)
    {
        try
        {
            query = "Insert into Newuser values(@UserName,@Password,@FullName)";
            cmd = new SqlCommand(query, conn);
            cmd.Parameters.AddWithValue("@UserName", txtUsername.Text);
            cmd.Parameters.AddWithValue("@Password", txtPassword.Text);
            cmd.Parameters.AddWithValue("@FullName", txtFullname.Text);
            conn.Open();
            cmd.ExecuteNonQuery ();
            conn.Close ();
        }
        catch(Exception ex)
        {
            lblErrors.Text =ex.Message.ToString();   
        }
 
 
    }

<title>New User Registration</title>
     <script type ="text/javascript" language ="javascript" >
     function LenofPassword()
     {
     var Password=document.getElementById("txtPassword");
 
       if(Password.value == "")
      {
        alert("Password should not be empty");
        Password.focus();
        return false;
       }
 
       if (Password.value.length <= 6 )
       {
        alert("Password length should be greater than 6");
        Password.focus();
        return false;
                  }
 
 
      var ConfirmPass=document.getElementById("txtConfirmPass");
          if(ConfirmPass.value == "")
      {
        alert("Confirm Password should not be empty");
        ConfirmPass.focus();
        return false;
            }
 
      if( Password.value != ConfirmPass.value)
      {
       alert(" Password  & Confirm Password do not match");
       return false;
       }
}

try
{
  query = "Insert into Newuser Select @UserName,@Password,@FullName Where Not Exists (Select * From NewUser x Where x.[UserNameColumn] = @UserName) Select Cast(@@ROWCOUNT as int) As Result";
  cmd = new SqlCommand(query, conn);
  cmd.Parameters.AddWithValue("@UserName", txtUsername.Text);
  cmd.Parameters.AddWithValue("@Password", txtPassword.Text);
  cmd.Parameters.AddWithValue("@FullName", txtFullname.Text);
  conn.Open();
  int rowCnt = Convert.ToInt32(cmd.ExecuteScalar());
  conn.Close ();
}
catch(Exception ex)
{
  lblErrors.Text =ex.Message.ToString();   
}