C++ Tutorial/Class/class prototype

Class prototype

<source lang="cpp">#include <iostream.h>

1. include <math.h>

class A; class B { int sum; public:

   B(){ sum=1;}
   B(int a,int b){sum=a*a+b*b;}
   int Larger(B b,A a);

}; class A //B must be before A, for A references the B::Larger() { friend int B::Larger(B b,A a);//use B::Larger()! private:int num; public:

   A(){num=1;}
   A(int a,int b){num=4*a+b;}
   void Display(void){cout<<num<< endl;}

}; int B::Larger(B b,A a) {

return (b.sum > a.num);

} int main(void) {

   B objB(1,2);
   A objA(3,3);
   if(objB.Larger(objB,objA)) {
       cout << "B obj is Larger , the small num is ";
       objA.Display();
   }else{
       cout << "B obj is not Larger\n";
   }
   return 0;

}</source>

B obj is not Larger