Grams measures mass... but cups is a measurement of volume.
You can't really compare the two as the gram is a weight measurement and a cup is a volume measurement. However in liquid conversions 1 litre of water is 1000 grams and 1 cup is 1/4 of a litre so...
in one cup of what?in an Australian measuring cup, 250g
240 grams
170g per cup of dry quinoa according to peertrainer http://www.peertrainer.com/DFcaloriecounterB.aspx?id=5912