Insert ComboBox selected value into table specific column?

Hi,

 

     I want to insert debit and credit values into the database table based on Combobox Selected Values.My ComboBox consists of Cr. and Dr. items and the Database table columns are Id,Name,Debit and Credit.When I select Debit from ComboBox and enter amount 1000 (in textbox) then the table Debit column should display as 1000Dr and the Credit column should be null like wise If I select Credit from ComboBox and enter amount 500 then the Credit column should display as 500Cr.(Debit column should be null).

         Here is Example

Id       Name      Debit           Credit

 1        Ram         1000Dr.        NULL

 2        Ravan       NULL           500Cr.

              How to write code for this?

Thanks in advance.