Three important differences:
* The first feature is the prototype - writing the parameter types as
a part of the function declaration. Prototypes make it easy for
a compiler to check function use with definition.
* Second feature is addition of new keywords -
+ enum for enumerated types
+ const
+ volatile
+ signed
+ void
And the 'entry' keyword was retired.
* Third category is of "silent changes" - some features that still
compiles, but now has a slightly different meaning. For example,
now that the preprocessing rules are more tightly defined, there's
a new rule that adjacent string literals are concatenated.