How to save selected item from drop down list into choice field

Question

Actually am fetching data from list to my drop down list(ddlseverity).

I want to get selected value from drop-down and display the value in choice filed in SharePoint list. after click submit button selected item will not be inserted into choice filed How can I achieve this?

SPFieldChoice fieldChoice = (SPFieldChoice)list.Fields.GetFieldByInternalName
                        (itemToAdd.Fields.Add(ddlpriority.Text, SPFieldType.Choice, true));
                        string[] types = { ddlpriority.Text };
                        fieldChoice.Choices.AddRange(types);
                        fieldChoice.Update();

Answer 1

Based on your comment, I got that you wish to create a new column every time. So try something like following

 list.Fields.Add("Your Field Name", SPFieldType.Choice, false);
 SPFieldChoice col = (SPFieldChoice) list.Fields["Your Field Name"];

 col.Choices.Add("option 1");
 col.Choices.Add("option 2");
 col.DefaultValue = "option 1"; 

 col.update(); 
 list.update();