Midterm Exam (2)
C++ Programming
NCNU CSIE

Date: March 30th, 2012
Time: 09:10-11:00
Open book; turn off computer & mobile phone

1. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
   
   // data member of a class
   #include <iostream>
   using std::cout;
   
   class CRational
   {
       int numerator;
       int denominator;
   
       CRational(int n, int d = 1): numerator(n)
       { denominator = d; }
   
       void Print()
       { cout << numerator << '/' << denominator; }
   };
   
   int main()
   {
       CRational a(1,2);
       CRational b(a);
       a = CRational(1,3);
       b.Print();
       return 0;
   }
   
   
   
2. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
   // Constructor
   #include <iostream>
   using std::cout;
   
   class CRational
   {
       int numerator;
       int denominator;
   
   public:
       CRational(int n, int d = 1): numerator(n), denominator(d)
       { cout << "Constructor called for ";
         Print();
         cout << '\n';
       }
   
       void Print()
       { cout << numerator << '/' << denominator; }
   };
   
   int main()
   {
       CRational a(1,2);
       CRational b(a);
       a = CRational(1,3);
       b.Print();
       return 0;
   }
   
   
   
3. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
   

   // data member of a class
   #include <iostream>
   using std::cout;
   
   class CRational
   {
       int numerator;
       int *denominator;
   
   public:
       CRational(int n, int d = 1): numerator(n)
       { denominator = new int(d); }
   
       void Print()
       { cout << numerator << '/' << *denominator; }
   };
   
   int main()
   {
       CRational a(1,3);
       CRational b(a);
       a = CRational(1,4);
       b.Print();
       return 0;
   }
   
   

   
   
4. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).

   // data member of a class
   #include <iostream>
   using std::cout;
   
   class CRational
   {
   public:
       int numerator;
       int *denominator;
   
       CRational(int n, int d = 1): numerator(n)
       { denominator = new int(d); }
   
       void Print()
       { cout << numerator << '/' << *denominator; }
   };
   
   int main()
   {
       CRational a(1,3);
       CRational b(a);
       *(a.denominator) = 4;
       b.Print();
       return 0;
   }
   
   

5. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).

   // Copy Constructor
   #include <iostream>
   using std::cout;
   
   class CRational
   {
       int numerator;
       int denominator;
   
   public:
       CRational(int n=0, int d=1): numerator(n), denominator(d) {}
   
       void operator=(CRational a) // What should be the return type?
       { numerator   = a.numerator;
         denominator = a.denominator;
       }
   
       void Print()
       { cout << numerator << '/' << denominator; }
   };
   
   int main()
   {
       CRational a(1,2);
       CRational b = a;		// Copy constructor is called
       b.Print();
       return 0;
   }
   
   

6. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
   

   // Copy Constructor
   #include <iostream>
   using std::cout;
   
   class CRational
   {
       int numerator;
       int denominator;
   
   public:
       CRational(int n=0, int d=1): numerator(n), denominator(d) {}
       CRational(CRational& a): numerator(1), denominator(1) {}
   
       void operator=(CRational a) // What should be the return type?
       { numerator   = a.numerator;
         denominator = a.denominator;
       }
   
       void Print()
       { cout << numerator << '/' << denominator; }
   };
   
   int main()
   {
       CRational a(2,3);
       CRational b = a;            // Copy constructor is called
       b.Print();
       return 0;
   }
   
   

7. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
   

   // Operator Overloading
   #include <iostream>
   using std::cout;
   
   class CRational
   {
       int numerator;
       int denominator;
   
   public:
       CRational(int n=0, int d=1): numerator(n), denominator(d) {}
       CRational(CRational& a): numerator(1), denominator(1) {}
   
       void operator=(CRational a) // What should be the return type?
       { numerator   = a.numerator;
         denominator = a.denominator;
       }
   
       void Print()
       { cout << numerator << '/' << denominator; }
   };
   
   int main()
   {
       CRational a(3,4);
       CRational c = b = a;        // Copy constructor is called
       c.Print();
       return 0;
   }
   
   
   

8. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
   

   // Operator Overloading
   #include <iostream>
   using std::cout;
   
   class CRational
   {
       int numerator;
       int denominator;
   
   public:
       CRational(int n=0, int d=1): numerator(n), denominator(d) {}
       CRational(CRational& a): numerator(1), denominator(1) {}
   
       CRational& operator=(CRational& a)  // What should be the return type?
       { numerator   = a.numerator;
         denominator = a.denominator;
       }
   
       void Print()
       { cout << numerator << '/' << denominator; }
   };
   
   int main()
   {
       CRational a(3,4);
       CRational c , b ;   // Copy constructor is called
       c = b = a;
       c.Print();
       return 0;
   }
   
   

   
   
9. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
   

   // When is Destructor called?
   #include <iostream>
   using std::cout;
   
   class CData
   {
   private:
       static int count;
   public:
       CData()  { ++count; }
       ~CData() { --count; }
       void ShowIt() { cout << count << '\n'; }
   };
   
   int CData::count = 0;
   
   void test1()
   {
       CData htc;
       htc.ShowIt();
   }
   
   void test2()
   {
       CData iphone[4];
       iphone[0].ShowIt();
   }
   
   int main()
   {
       test2();
       test1();
       return 0;
   }
   
   

10. (10%) Determine whether the following code has syntax erros or not.  If it is correct, predict its output.  If it is incorrect, point out the mistake(s).
    

    // Operator Overloading
    #include <iostream>
    using std::cout;
    class CRectangle
    {
            int left, top, right, bottom;
    
            int Area() const
            { return (right-left)*(bottom-top); }
    public:
            CRectangle(int x1, int y1, int x2, int y2): 
    		left(x1), top(y1), right(x2), bottom(y2) {}
            bool operator>(const CRectangle& aRect) const
            { return Area() > aRect.Area(); }
    };
    
    int main()
    {
            CRectangle pool(10, 20, 30, 50);
            CRectangle hut(20,30, 45, 50);
            if (pool > hut)
                    cout << "The pool is bigger.\n";
            else
                    cout << "The hut is bigger.\n";
    }