C# .NET - Sending a datasructure to a database? [C#]

Dear Reader,

I got a problem with my code i want to send information taken from a twincat plc system to my database.
Everything works fine expect for the last part the actual sending to the DB. If you look @ the code go to this part tbComplexStruct_Datavalues.Text = String.Format (It's on line 330)
There you can find all the datavalues i pick up out of the twincat system these has to be sended to a mysql db this happens @   private void Main2() (It's on line 261)  I really hope someone could help me out with this since i am messing arround with it for weeks. Thanks in advance.

The problem is in the highlighted lines below:

using (var conn = new MySqlConnection(cs))
270.      using (var cmd = conn.CreateCommand())
271.      {
272.      conn.Open();
273.      cmd.CommandText = "INSERT INTO actualvalues (a,b,c) VALUES ('structure.datavalues[0],'structure.Datavalues[1]','structure.Datavalues[2]')";
274.      cmd.ExecuteNonQuery();
275. 
276.      }

It should be like this:
using (var conn = new MySqlConnection(cs))
270.      using (var cmd = conn.CreateCommand())
271.      {
272.      conn.Open();
273.      cmd.CommandText = string.Format("INSERT INTO actualvalues (a,b,c) VALUES ('{0},'{1}','{2}')", 
structure.datavalues[0], structure.datavalues[1], structure.datavalues[2]);
274.      cmd.ExecuteNonQuery();
275. 
276.      }

And few other things that I observed:

a) Not sure why you have the for loop that runs for fixed iterations (5).
Line#267 - for (int i = 0; i < 5; i++)

b) It is a bad practice to name methods like Main2. Provide a meaningful name.
Line# 261 private void Main2()

c) And these lines can be refactored to something more readable.
Line# 327 tbComplexStruct_Datavalues.Text = String.Format...to Line# 357 structure.Datavalues[100]

StringBuilder temporaryStringBuilder = new StringBuilder();
for (int counter = 0; counter < 100; counter++)
{
                temporaryStringBuilder.Append(string.Concat(string.Format("{0:d}", structure.Datavalues[counter]), ","));
}
string finalString = temporaryStringBuilder.ToString().Substring(0, temporaryStringBuilder.Length -1);

Hope this helps.