You seem to have two textViews one with
id = textView51
id = textViewC51
in your onCreate you are trying to find the first textview and pass it to another
textViewC51 = (TextView) findViewById(R.id.textView51);
Try to change the previous line with:
textViewC51 = (TextView) findViewById(R.id.textViewC51);
and see if it works for you.