How can I choose a random string from an array - Arduino 101

I am trying to write code for my Arduino Uno with Adafruit MP3 Music Maker Shield that plays a randomly selected song from an array whenever it is turned on, I have very little experience with both C++ and Arduino, but what seems like a simple task (retrieving a randomly picked string from an array) is surprisingly difficult.

Here is a sample of the code I have:

String str,song={"track001.mp3", "track002.mp3", "track003.mp3"};
str = str + song[random(0,10)];
musicPlayer.playFullFile(str);

When I try to compile I get the error: "could not convert '{"track001.mp3", "track002.mp3", "track003.mp3"}' from '' to 'String'"

I want to figure out what is causing the hour and how I can get the code I want. Any and all help would be appreciated, more code and other information can be given upon request, thanks!