C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 6:
6.1 Is C++ a practical language?
6.2 Is C++ a perfect language?
6.3 What's the big deal with OO? Updated!
6.4 What's the big deal with generic programming?
6.5 Is C++ better than Ada? (or Visual Basic, C, FORTRAN, Pascal, Smalltalk, or any other language?)
6.6 Who uses C++?
6.7 How long does it take to learn OO/C++?
6.8 What are some features of C++ from a business perspective?
6.9 Are virtual functions (dynamic binding) central to OO/C++?
6.10 Why do virtual functions (dynamic binding) make a big difference?
6.11 Is C++ backward compatible with ANSI/ISO C?
6.12 Is C++ standardized? Updated!
6.13 Where can I get a copy of the ANSI/ISO C++ standard?
6.14 What are some "interview questions" I could ask that would let me know if candidates really know their stuff?
6.15 What does the FAQ mean by "such and such is evil"?
6.16 Will I sometimes use any so-called "evil" constructs?
6.17 Is it important to know the technical definition of "good OO"? Of "good class design"?
6.18 What should I tell people who complain that the word "FAQ" is misleading?
6.19 How can I help make the C++ FAQ even better??!??
[6.11] Is C++ backward compatible with ANSI/ISO C?

Almost.

C++ is as close as possible to compatible with C, but no closer. In practice, the major difference is that C++ requires prototypes, and that f() declares a function that takes no parameters (in C, a function declared using f() can be passed an arbitrary number of parameters of arbitrary types).

There are some very subtle differences as well, like sizeof('x') is equal to sizeof(char) in C++ but is equal to sizeof(int) in C. Also, C++ puts structure "tags" in the same namespace as other names, whereas C requires an explicit struct (e.g., the typedef struct Fred Fred; technique still works, but is redundant in C++).