April 1999
OP216: OBJECT-ORIENTED PROGRAMMING

QUESTION 3

Total Marks: 20 Marks

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GRADE A
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(a) One form of Polymorphism in C++ is operator overloading.
(i) Explain, using an appropriate example, the term operator overloading. [3]
(ii) Consider the polymorphic expression 5 == 5.0 in C++. What form of polymorphism is this an example of? Explain your answer. [2]
(i) Overloading allows same function name or operator to be used on different argument type. The function is called based on its signature. The number and type of argument in the parameter list.

(ii) Coercion. The two argument are of different types.

 
Consider the declaration of the class String below. You are to write overloaded operator functions for strings.

class String {
public:
   int length();     // Return the length of the
                     // string
   char char_at(int);   // Return the character at
                        // the given position
   void update_at(int, char); // Update the character
                            // at the given position
}

 
(b) Give an implementation of the overloaded operator < that takes two strings by reference and returns 1 if the first is less than the second, or 0 otherwise. [2]
int operator < (String &f, String&s)
{  int j = f.length();
   int k = s.length();
   int i = -1;
   Do {
      i++;
      if (f.char_at(i) < s.char_at(i))
         return 1;
   }
   while (i < j && i < k);
   return 0;
};

 
(c) Give the implementation of the overloaded operator == that takes two strings by reference and returns 1 if they are equal, or 0 otherwise. [6]
int operator == (String &f, String&s)
{  int j = f.length();
   int k = s.length();
   if (j != k)
      return 0;
   int i = -1;
   Do {
      i++;
      if (f.char_at(i) != s.char_at(i))
         return 0;
   }
   while (i < j);
   return 1;
};

 
(d) Give an implementation of the function cmp that takes two strings by reference and returns -1 if the first is less than the second, 0 if they are equal, or 1 is the first is greater than the second. [4]
int String cmp (String &f, String&s)
{  if (f < s)
      return -1;
   else if (f == s)
      return 0;
   else
      return 1;
};