I cannot be sure, but I believe the MQL5 documentation is more relevant now. Also check out the following thread for details of the changes:
MetaTrader 4 Build 600 with Updated MQL4 Language and Market of Applications Released <https://www.mql5.com/en/forum/149271/>
etn:
There isn't an updated book and I suspect there will not be one . . . you should be asking when the Documentation will be updated.
Can someone please let me know where to find the updated MQL4 Book?
I need to know what changes I had to do with my codes when I update my MT4 to Build 600.
The information available in https://book.mql4.com/ is still showing the old version before the recent major change to build 600.
Thanks.

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Can someone please let me know where to find the updated MQL4 Book?
I need to know what changes I had to do with my codes when I update my MT4 to Build 600.
The information available in https://book.mql4.com/ is still showing the old version before the recent major change to build 600.
Thanks.