#include <iostream>
using namespace std;

class base {
public:
    static const int i = 16;
};
const int base::i;


int main()
{

    return 0;
}

А>#include <iostream>
А>using namespace std;

А>class base {
А>public:
А>    static const int i = 16;
А>};
А>const int base::i;


А>int main()
А>{

А>    return 0;
А>}
А>

class base
{
public: static const int i = 16;
};

class base
{
public: static const int i;
};

const base::i = 16;

class base
{
public: 
    static const int i = 16;
};

C:\Program Files\Microsoft Visual Studio\MyProjects\1\1.cpp(7) : error C2258: illegal pure syntax, must be '= 0'
C:\Program Files\Microsoft Visual Studio\MyProjects\1\1.cpp(7) : error C2252: 'i' : pure specifier can only be specified for functions

class base
{
public: 
    enum { i = 16 };
};

9.4.2 п.4
If a static data member is of const integral or const enumeration type, its declaration in the class definition can specify a constant-initializer which shall be an integral constant expression (5.19). In that case, the member can appear in integral constant expressions. The member shall still be defined in a namespace
scope if it is used in the program and the namespace scope definition shall not contain an initializer.