If you are programming in Visual Basic, you can use the CBool function to convert the string representation of a number to a Boolean value. 0 is converted to false, and the string representation of any non-zero value is converted to true.
Nick is trying to figure out who Gatsby really is. Nick hears these rumors about gatsby, how he was a German spy, a murderer, etc.. Nick is disappointed with Gatsby because Gatsby has little too say. Nick wants Gatsby to tell him who he really is, what he does, where is he from. Unsurprisingly, Gatsby does not tell him, even though they talk a lot and hang out a lot. Nick is trying to figure out who Gatsby really is.
His obsession has driven him to accomplish much of what he has; although Gatsy tries to draw him in to some of his businesses, Nick is too moral and sensible for such a thing. Ultimately, Nick is the only one who really cares about Gatsby in death; he learns about Gatsby and wants not to live the way he lives.