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C++ and OOPS Sample Question

4. class base
           {
           public:
           	void baseFun(){ cout«"from base"«endl;}
           };
    class deri:public base
           {
           public:
           	void baseFun(){ cout« "from derived"«endl;}
           };
   void SomeFunc(base *baseObj)
   {
           baseObj->baseFun();
   }
   int main()
   {
   base baseObject;
   SomeFunc(&baseObject);
   deri deriObject;
   SomeFunc(&deriObject);
   }

   Answer:

   from base
   from base

   Explanation:

   As we have seen in the previous case, SomeFunc expects a pointer to a base class. Since a pointer to a derived class object is passed, it treats the argument only as a base class pointer and the corresponding base function is called.

5. class base
           {
           public:
           	virtual void baseFun(){ cout«"from base"«endl;}
           };
    class deri:public base
           {
           public:
           	void baseFun(){ cout« "from derived"«endl;}
           };
   void SomeFunc(base *baseObj)
   {
           baseObj->baseFun();
   }
   int main()
   {
   base baseObject;
   SomeFunc(&baseObject);
   deri deriObject;
   SomeFunc(&deriObject);
   }

   Answer:

   from base
   from derived

   Explanation:

   Remember that baseFunc is a virtual function. That means that it supports run-time polymorphism. So the function corresponding to the derived class object is called.

6. void main()
   {
   	int a, *pa, &ra;
   	pa = &a;
   	ra = a;
   	cout «"a="«a «"*pa="«*pa «"ra"«ra ;
   }

   Answer:

   Compiler Error: 'ra',reference must be initialized

   Explanation:

   Pointers are different from references. One of the main differences is that the pointers can be both initialized and assigned, whereas references can only be initialized. So this code issues an error.

7. const int size = 5;
   void print(int *ptr)
   {
   	cout«ptr[0];
   }
   
   void print(int ptr[size])
   {
   	cout«ptr[0];
   }
   
   void main()
   {
   	int a[size] = {1,2,3,4,5};
   	int *b = new int(size);
   	print(a);
   	print(b);
   }

   Answer:

   Compiler Error : function 'void print(int *)' already has a body

   Explanation:

   Arrays cannot be passed to functions, only pointers (for arrays, base addresses) can be passed. So the arguments int *ptr and int prt[size] have no difference as function arguments. In other words, both the functoins have the same signature and so cannot be overloaded.

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