Why does main return a value of type int?

I'm not going to get into the reasons why the main function return a value of type int here.  (That is a topic for a more advanced course.) 

Suffice it to say that this requirement manifests itself in two ways in Listing 1:

• Specification of a return type of int immediately before the name of the function (more on this later)
• Inclusion of a return statement at the end of the function that causes a value of type int to be returned.  (In this program, the returned value is 0.)