Why do giraffes have long neck..  

Good question dude but the answer is very simple for this question. At the time of evolution even Giraffe had normal necks like as other animals have. But due to the evolution the neck of the Giraffe went on growing tall and now we can see the tall neck of this animal. The reason for this is that the giraffe wanted to eat fresh leaves of the tall trees and due to this the streching of neck took place and thus we can see long necks of them. Let me know if any further details you have.

Giraffes have long neck so that they get help in eating leaves :D... Maybe once a giraffe asked for a wish in a well that he had a long neck to eat those green green leaves XD

Actually the right answer is that giraffes have long necks so they can reach the top of the trees to eat leaves where other herbivores cannot reach. That is why they have long necks, and they adapted that way, if you look at a chart showing their ancestors they actually had shorter necks.

Actually, there is a right answer. It is based on evolution. The ancestral line of the giraffe all had shorter necks, but they got sequentially longer with the evolution of each species, because being able to reach vegetation in high places was a niche that had yet to be filled.

So, over time, the ancestors to the giraffe, as they kept reaching higher and higher for the vegetation in the trees, they began to produce offspring, some of which had longer necks than others. The offspring with longer necks had an advantage over the ones with shorter necks. Thus, the reproductive success of those with longer necks was higher, resulting in more offspring produced in subsequent generations that had longer necks, until finally, we had a new species, the giraffe. This did not happen overnight, but rather over millions of years' time.