MATLAB: How does the FFT zero pad

Question

I am using the Hilbert function for an analysis, and I would like to use the FFT method to get the imaginary part. What I am unsure of is how the FFT function is zero padding? I would like there to be an even number of zeros on each end of my data so that when I apply a window, my data are centered. Any help on this would be greatly appreciated.

example of code I'm using (i've attached an example mat file with the variable "prox")

a= hilbert(hann(length(prox)).*prox,2^8);

Answer 1

Y = fft(X,n);

is the same as

Xp=X;
Xp(length(X)+1:n)=0;
Y=fft(Xp);