title: C# Login Form - Retrieve database value corresponding to Username in Form 2 after signing in from Form1
body: <p>I have a C# form application. Form1 serves two objectives, one for Signing Up and other For Signin in. 
  Signup data includes Username, ID Number and Password which are saved in a database, also only Unique Username is allowed, i.e if a Username is already in use it cannot be used again.</p>
  
  <p>The signin requires Username and Password. But after Signing in, how to display the ID Number of the corresponding unique Username in a textbox on form2 is the problem. </p>
  
  <p>Below is my current code.</p>
  
  <pre><code>//for signing in
      private void button1_Click(object sender, EventArgs e)
      {
          if(textBox1.Text == "" || textBox2.Text == "")
          {
              MessageBox.Show("!!Please fill in both Username and Password!! ");
          }
          else
          {
              SqlConnection sqlcon = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=""C:\Users\Lenovo\Desktop\dev\C# .net\Aadi Paw Plethysmometer\Aadi Paw Plethysmometer\Database1.mdf"";Integrated Security=True");
              string query = "Select * from Signup where Username = '" + textBox1.Text.Trim() + "' and Password = '" + textBox2.Text.Trim() + "'";
              SqlDataAdapter sda = new SqlDataAdapter(query,sqlcon);
              DataTable dtbl = new DataTable();
              sda.Fill(dtbl);
              if (dtbl.Rows.Count &gt; 0)
              {
  
                  Form2 newForm = new Form2();
                  newForm.Show();
                  this.Hide();
  
              }
              else
              {
                  MessageBox.Show("Invalid username or password");
                  textBox1.Text = textBox2.Text = "";
              }
  
          }
      }
  
  //For Sign Up
  private void button2_Click(object sender, EventArgs e)
      {
          if (FirstName.Text == "" || SecondName.Text == "" || Username.Text == "" || Password.Text == "" || InstituteID.Text == "" || RInstituteID.Text == "")
          {
              MessageBox.Show("Kindly fill in all the specified fields.");
          }
          else if((InstituteID.Text != RInstituteID.Text) &amp;&amp; (Password.Text != RPassword.Text))
          {
              MessageBox.Show("Password Mismatch and Institute ID Mismatch. Please enter again...");
          }
          else if ((InstituteID.Text != RInstituteID.Text) &amp;&amp; (Password.Text == RPassword.Text))
          {
              MessageBox.Show("Institute ID Mismatch. Please enter again...");
          }
          else if ((InstituteID.Text == RInstituteID.Text) &amp;&amp; (Password.Text != RPassword.Text))
          {
              MessageBox.Show("Password Mismatch. Please enter again...");
          }
          else
          {
              using (SqlConnection sqlCon = new SqlConnection(connectionstring))
              {
                  sqlCon.Open();
                  //after connection is open, using following "if" code to check uniqueness of Username
                  string query2 = "Select * from Signup where Username = '" + Username.Text.Trim() + "'";
                  SqlDataAdapter sda = new SqlDataAdapter(query2, sqlCon);
                  DataTable dtbl2 = new DataTable();
                  sda.Fill(dtbl2);
                  if (dtbl2.Rows.Count &gt; 0)
                  {
                      MessageBox.Show("Username already in Use. Change Username and try Signing up again...");
                  }
  
                  else
                  {
                      SqlCommand sqlcmd = new SqlCommand("Useradd", sqlCon);
                      sqlcmd.CommandType = CommandType.StoredProcedure;
                      sqlcmd.Parameters.AddWithValue("@FirstName", FirstName.Text.Trim());
                      sqlcmd.Parameters.AddWithValue("@SecondName", SecondName.Text.Trim());
                      sqlcmd.Parameters.AddWithValue("@Username", Username.Text.Trim());
                      sqlcmd.Parameters.AddWithValue("@Password", Password.Text.Trim());
                      sqlcmd.Parameters.AddWithValue("@RPassword", RPassword.Text.Trim());
                      sqlcmd.Parameters.AddWithValue("@InstituteID", InstituteID.Text.Trim());
                      sqlcmd.Parameters.AddWithValue("@RInstituteID", RInstituteID.Text.Trim());
                      sqlcmd.ExecuteNonQuery();
                      MessageBox.Show("Sign Up is Successfull!");
                      clear();
                  }
  
              }
  
          }
      }
  </code></pre>