Can You Grow Marijuana In A Cup?

Depends on the size of the cup but a regular red party cup will work. Just fill it good soil and plant your seeds make sure they get some good sunlight or they will definitely die. Sunlight is key to growing marijuana. You might want to switch your plant out of that cup before it gets 3 weeks old or you plant will be really small.

You'd get about a bowl from a dixie cup.... The bigger you want the plant, the more structure it needs below the soil to maintain a substantial root system.
For great information, check out The Indoor Marijuana Horticulture Bible by Jorge Cervantes.

I'm sure your plant died because the first answer didn't tell you that you need to put some holes in the bottom of the cup so there is drainage when you water it. If there is no drainage at the bottom, water will most likely drown the plant.