CS 325 Software Development and Systems

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CS 325 Software Development and Systems
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Lecture 8

• Today
• Rational Class
• Friend Functions
• Chapter 6 Classes
• Chapter 7 More on classes
• Chapter 8 Operator Overloading
• Next Project
• Is on the website (cs.ua.edu/325) due Thursday,
  October 7 _at_ midnight

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Quick Review

• What goes in the specification?
• What do we call the file where the specification
  is stored?
• What goes in the implementation?
• An instance of a class is called
• What is the difference between the private
  section and the public section?

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Lets write a class for Rational Numbers

• Want to be able input rational numbers, output
  rational numbers, add rational numbers, multiply
  rational numbers,

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Want to be able to overload operators

• Well use friend functions to do this.
• Friend function an ordinary function that has
  access to the private parts of a class
• Prototype must be in class specification
• friend rtrn_type funcName(arguments)
• Prototype will be defined in class implementation
• rtrn_type funcName(arguments)

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Addition with rationals

• In public section of specification
• friend rational operator (rational, rational
  )
• In implementation
• rational operator (rational r1, rational r2)
  rational res
• res.n r1.n r2.d r2.n r1.d
• res.d r1.d r2.d

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Class Exercises

• Write a friend function that will allow us to
  overload the operator for multiplication
• Write a member function that will allow us to
  reduce a rational number

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Overloading ltlt gtgt

• Read and print integers easily
• int x
• cin gtgt x
• cout ltlt x ltlt endl
• Need same ability for our Rational class
• Rational r
• cin gtgt r
• cout ltlt r ltlt endl
• Overload ltlt and gtgt operators to work with
  Rationals (the Rational class)

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Background on cin and cout

• Both are instances of a class (objects)
• cin an instance of input stream class
• cout an instance of output stream class
• ltlt and gtgt are binary operators
• int a, b
• cin gtgt a // reads value into a
• cingtgtb // reads value into b
• Need to let these two classes see a Rational

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Overloading ltlt gtgt

• Need to let the I/O classes have access to the
  private part of our Rational class
• input operation needs to set num and den
• output operation needs to read num and den
• I/O operators will also be friend functions of
  the class Rational

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Syntax for overloading ltlt gtgt

• friend ostream operatorltlt(ostream os, Rational
  r)
• os ltlt r.nltlt "/" ltlt r.d return os
• Line 1
• 1. The method is a friend of class Rational
• 2. The method returns an ostream (modified
  output stream)
• 3. The operator we are overloading is ltlt
• 4. The two arguments are the output stream the
  Rational to output
• Line 2
• 1. On the output stream, print numerator, /,
  denominator
• 2. Return the modified output stream (now
  includes these characters)

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Class Exercises

• Modify your input/output member functions to be
  friend functions that overload the gtgt and ltlt
  operators.

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End of Lecture 8

• Next Time Overloading operators using member
  functions