Do the static (class) variables necessarily have to be const? [duplicate]

This question already has an answer here:

• Why do non-const, non-int/enum static data members have to be initialized outside the definition? 5 answers

I tried compiling this in visual studio:

class A {
    int a;
    static int b = 0;
    public:
        A(int x) { a = x; }
        void changeA(int x) { a = x; }
        int getA() { return a; }
};

And it gives me the following error:

error C2864: 'A::b' : a static data member with an in-class initializer must have non-volatile const integral type

What seems to be the problem officer?