Calculate the textbox value based on the value of combobox ? ( wpf )

[Member_14680372]

I have a small program, because I'm new, my program is to bring data from sql sever to textbox via combobox option and use the value shown in that textbox to calculate the + I have made it to the step of putting up the data, now thanks to you to help me with the value calculation in the textbox, thank you for your help.

xaml code :

[Lost User]

What is the problem, and where does it occur?

[Member_14680372]

https://www.upsieutoc.com/image/FSfuXK

[Richard Deeming]

Member 14680372 wrote:

string sql = " select * from comboboxnew where code = '" + comboBox1.SelectedItem + "';";

Don't do it like that! Your code is vulnerable to SQL Injection[^]. NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query. Everything you wanted to know about SQL injection (but were afraid to ask) | Troy Hunt[^] How can I explain SQL injection without technical jargon? | Information Security Stack Exchange[^] Query Parameterization Cheat Sheet | OWASP[^]

private void ComboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
using (SqlConnection con = new SqlConnection("Data Source=LEAN-22\\SQLEXPRESS;Initial Catalog=LUAT;Integrated Security=True"))
using (SqlCommand cmd = new SqlCommand("SELECT TOP 1 * FROM comboboxnew WHERE code = @code;"))
{
cmd.Parameters.AddWithValue("@code", Convert.ToString(comboBox1.SelectedItem));

    con.Open();
    
    using (SqlDataReader myreader = cmd.ExecuteReader(CommandBehavior.CloseConnection))
    {
        if (myreader.Read())
        {
            string code = myreader.GetInt32(0).ToString();
            string pieces = myreader.GetInt32(1).ToString();
            string layers = myreader.GetInt32(2).ToString();
            string productionpieces = myreader.GetInt32(3).ToString();
            string seccond = myreader.GetInt32(4).ToString();
            
            txtcode.Text = code;
            txtpieces.Text = pieces;
            t