A Question about ##

hi,all
   I have a program about ## ,which is the following.
=========================================================
#include <iostream>
using namespace std;

class CMyClass {
public:
   static int m_i;
public:
 CMyClass(){
  m_i++;
 }
};

#define NEWW(i)   CMyClass *a_##i=new CMyClass();
#define PPR(i)   cout<<a_##i->m_i<<endl
#define F(i)   F_##i()
int CMyClass::m_i = 0;


int F_0()
{
 cout<<"F0"<<endl;
 return 1;
}

int F_1()
{
 cout<<"F1"<<endl;
 return 1;
}

int F_2()
{
 cout<<"F2"<<endl;
 return 1;
}

int F_3()
{
 cout<<"F3"<<endl;
 return 1;
}

void FF(int i){
 int a;
 a=i;

 switch(a){
  case 0:{
   F(0);
   break;
  }
  case 1:{
   F(1);
   break;
  }
  case 2:{
   F(2);
   break;
  }
  case 3:{
   F(3);
   break;
  }

 }

}

void NEW(int i){
 int a;
 a=i;

 NEWW(i);
 PPR(i);

}

int main()
{
 for(int i=0;i<10;i++){
  NEW(i);
 }
 for(int i=0;i<4;i++){
  FF(i);
 }

   return 0;
}

===========================
The question is the I can call NEWW(i) in function void NEW(int i)
But failed in processing function void FF(int i)?
If we write void FF(int i) as:
void FF(int i){
    F(i);
}
It will fail.

Compiler : VS2005