What are the differences between the main() function and other user-defined functions in C?

Question

The main() function is known as a user-defined function in C. But how does it differ from other user-defined functions?

Answer 1

The main() function is just a regular user-defined function — but it has two special properties:

• In a hosted implementation (the normal type), it is the function called by the start-up code.
• In C99 and later, if execution falls off the end of main() without an explicit return statement, it is equivalent to return 0;. No other function gets that privileged treatment.

See also What should main() return in C and C++? for some caveats about the second point.