Here is the example of future option in John Holl's book
Options, Futures and Other Derivatives 9th page 384.
I don't understand that when you exercise the future call option, you enter a long position of a future, then what's the price of your future? Actually, I don't much understand the
P&L on future when you close out the future after exercise.
For my understand, you hold a long position of future with price $331,$ when you exercise, the price become $330,$ then you should
lose the money
earn the money in the book, so where is my misunderstand?