Why does `int ;` compile fine in C, but not in C++?

Question

Consider the following program (see live demo here).

#include 
int main(void)
{
      int ;  // Missing variable name
      puts(\"Surprise\")         


        

Answer 1

The syntax of declaration is defined as (omitting init-declarator-list and init-declarator):

C11 6.7 Declarations

declaration:
    declaration-specifiers init-declarator-list opt ;
    static_assert-declaration
declaration-specifiers:
    storage-class-specifier declaration-specifiers opt
    type-specifier declaration-specifiers opt
    type-qualifier declaration-specifiers opt
    function-specifier declaration-specifiers opt
    alignment-specifier declaration-specifiers opt

Note that declaration-specifiers is defined recursively, but each with an opt indicates it's optional.

Also, the following clause 6 states:

The declaration specifiers consist of a sequence of specifiers that indicate the linkage, storage duration, and part of the type of the entities that the declarators denote. The initdeclarator-list is a comma-separated sequence of declarators, each of which may have additional type information, or an initializer, or both. The declarators contain the identifiers (if any) being declared.

Note the words if any.