declaration of friend classes ,size of heap in c++

Declaration of friend classes

 class XYZ  
  {  
 int x;  
 public:  
 };  
 class ABC  
 {  
 int y;  
 public:  
 friend class XYZ;  
 };  
 /////////////  
 class ABC; //forward declaration  
 class XYZ  
 {  
 int x;  
 public:  
 void fun(){  
 ... ABC tmp;  
 ... tmp.y=10; //legal  
 }  
 };  
 class ABC  
 {  
 int y;  
 public:  
 friend class XYZ;  
 void fun()  
 {  
 ... XYZ tmp;  
 ... //tmp.y=10; Illegal  
 }  
 };  
 //Size of heap in c++  
 #include  
 #include  
 int main()  
 {  
 char *a=(char *)0;  
 int (*fun)()=main;  
 printf("%u ",fun);  
 return(0);  
 }