java.lang.NullPointerException on retrieving data from database in android

I am trying to retrieve data from SQLite database. code is working fine for all other variables but when it reach at the Pre_result then it throw excetion.

<pre class="default prettyprint prettyprinted">

    try{
                    SQLiteDatabase dbR = DB_Help.getReadableDatabase(); 
                    String[] projection = {DB_Help.Pre_ID,DB_Help.Pre_Query,DB_Help.Pre_Results};

                    Cursor c = dbR.query(DB_Help.Previous_Table,     
                              projection,      
                              null,     
                              null,     
                              null,     
                              null,     
                              null      
                              );

                    int ii=c.getColumnIndex(DB_Help.Pre_ID);
                    int iq=c.getColumnIndex(DB_Help.Pre_Query);
                    int ir=c.getColumnIndex(DB_Help.Pre_Results);
                    Log.e("C : ", String.valueOf(c));
                    res_title.setText("ID : "+ii+ " Q : "+iq+" R : "+ir);
                    for (c.moveToFirst();!c.isAfterLast();c.moveToNext()) {
                         query_txt.setText(c.getString(iq));

                         // Code work fine untill this line.
                         // this line throwing exception of null pointer, 
                         res_txt.setText(c.getString(ir));
                    }

                c.close();

            }catch(Exception e){
                Log.e("GetResults", "Error in Data Retrival : "+e.toString());
            }</pre>