Hi! I can see why you're worried, as vomiting blood is never a good sign...
I'm not much of an expert on stomach cancer, but I am a Health Science major, so I just looked in one of my books. According to it, the symptoms of stomach cancer are:
Unintended weight loss and lack of appetite
* Abdominal pain
* Vague discomfort in the abdomen, usually above the navel
* A sense of fullness in the upper abdomen, just below the chest bone after eating a small meal. Doctors call this early satiety.
* Heartburn, indigestion, or ulcer-type symptoms
* Vomiting, with or without blood
* Swelling of the abdomen due to accumulation of fluid and cancer cells. Doctors call this malignant ascites.
Also, stomach cancer doesn't usually show symptoms until it's in the advanced stages.
How long has your dad been feeling this way? If it's been more than a few days, he should go to the doctor.
I hope he gets better!