I'm pretty new to digital signal processing, my degree touched on it briefly, but it's interested me since. I am trying to determine the fundamental frequency of a guitar note played into a mbed LPC1768.
I am currently reading the analog signal in and storing it as an array of floats, the data is currently sampled at 1000Hz for 1 second.
By plotting the values against 1-1000 (milliseconds) I can create this graph. This is a ~1 second snippet of an E String being played.

I was hoping someone could give me a few pointers on the best library to use to convert my 1D array into a form which would give me the frequencies involved in this converting this data from time-domain to frequency-domain.
I have seen some libraries but I can't figure out how to actually implement them due to a lack of examples.