Difference between iPad and iPhone 4

I have been really interested in buying an iPhone 4 for a long time, but now I am also thinking of owning an iPad. And I am wondering what's a major difference between an iPad and iPhone 4. Please help me finally choose to buy it.Well. The iPhone is a phone and the iPad is a portable computer. This is the main difference.And you can put the iPhone 4 in your shirt pocket. But the iPad that is huge