How can i Add or substract on data already existing in mysql Db.(c#)

Question

How can i Add or substract on data already existing in mysql Db.(c#)

Error Message

try
            {
                conn = new MySqlConnection(cs.ConnString);
                conn.Open();
                cmd = new MySqlCommand();
                cmd.Connection = conn;
                cmd.CommandText= "update Compte set Solde_Actuel_$ = Solde_Actuel_$ - " + MontantDollars_AAS_txt.Text + " WHERE Code_Compte='" + Code_txt.Text + "'";
                cmd.ExecuteReader();
                conn.Close();                 

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

Answer 1

I use MSSQL server and your code works for me. The data were successfully updated. I think there may be a problem with runtime value of your .Text variable

    try
    {
        var propertyText = "Test2";

        var conn = new SqlConnection(_configuration.GetConnectionString("Default"));
        conn.Open();
        var cmd = new SqlCommand
        {
            Connection = conn,
            CommandText = "update Terminals set Zipcode = " + 123 + " WHERE Name='" + propertyText + "'"
        };
        cmd.ExecuteReader();
        conn.Close();
    }