S-Function encoder_slsp_mega code explanation

Hello,

i want to ask about several commands on encoder_slsp_mega blocks that i got from this link : http://www.mathworks.com/matlabcentral/fileexchange/39354-device-drivers . and i still don't get about this command:

typedef struct { int pinA; int pinB; int pos; int del;} Encoder;    
volatile Encoder Enc[3] = {{0,0,0,0}, {0,0,0,0}, {0,0,0,0}};

what are "typedef struct" and "Enc[3]" function means?also i confused about "global variables" that mentioned in sfunction guide. From the guides tells me that all parameter must be wrote on global variables on library pane. i was tried to create my own encoder block from arduino simple code but i got error in the end of compiling. it said that my parameters was not declare, although i had put it on the discrete update pane. can anybody tells me how to write global variables in s-function pane from arduino code.

All the answers will be appreciate. Thanks alot

Aldiaz