都是一杯.
但:
1、cup通常指带柄的瓷杯,用来喝茶、牛奶、咖啡等,a cup of 指一杯的量,还可以用作比赛用的金杯、银杯.
如：Please pass me a cup of tea.
Who own the cup?
2、glass通常指玻璃杯,用以饮酒、喝水等.There is a glass on the table.
Will you have a glass of a beer?