Im17yr old smoked for5yrs, stopped smoking for4days i had dry cough for almost a month & i already spit blood.is there chance that i have lung cancer?

Probably not serious: Congratulations for stopping smoking: hang in there! Cancer is exceedingly rare at your age of 17, regardless of smoking history. Bronchitis and minor irritation of the airways can cause slight bleeding -- probably not serious unless it recurs or lots of blood. To be completely safe, see your doctor. But don't lose a lot of sleep in the meantime; probably this isn't serious.