After:

class power
{
   public:
      void compute()
      {
         cout << "Enter a number" << endl;
         cin >> number;

         result = calcPower( number );

         cout << "The power of " << number << " is " << result << endl;
      }

      virtual int calcPower( int number ){
         return number;
      }

   protected:
      int number;
      int result;
};

class square: public power
{
   public:
      virtual int calcPower( int number ){
         return number * number;
      }
};