Programming

1
Programming

• Abstract Data Types

2
Review class

• Name one reason why we need the class construct.
• Why do we need "inspector functions" to read the
  values and "mutator functions" to modify values?

Abstract (user-defined) data types
Private data members
3
Review class

• Is there a way to avoid all these hassles, for
  instance
• void main()
• Temperature temp
• cout ltlt temp.degree ltlt ' ' ltlt temp.scale ltlt
  endl // no inspectors
• temp.scale 10 // no mutators
• temp.degree 'c'
• If yes to above, why we need all the hassles of
  inspector and mutator functions?

Public data members!
Information hiding
4
Abstract Data Type

• An Abstract Data Type is a class with some
  special restrictions.
• These restrictions can make programming easier.
• One of these restrictions is called information
  hiding, and it helps avoid common problems (e.g.,
  a denominator of zero should not be allowed in
  rational numbers).
• In information hiding, the user should not be
  allowed to access the data members directly (they
  should be private).
• An Abstract Data Type is used in Object-Oriented
  Programming (COMP151).

5
Rational Review

• Multiplication
• Division

• Rational number
• Ratio of two integers a/b
• Numerator over the denominator
• Standard operations
• Addition
• Subtraction

6
Rational Representation

• Represent a numerator and denominator
  with two int data members
• NumeratorValue and DenominatorValue
• Data members private (information hiding)
• Public arithmetic member functions
• Rational addition, subtraction, multiplication
  and division
• Public relational member functions
• Equality and less than comparisons

7
Rational Representation

• Public functions
• Construction
• Default construction
• Rational r
• Specific numerator and denominator construction
• Rational r(3, 4)
• Copy construction (provided automatically)
• Rational r(t) Rational r t
• Assignment (provided automatically)
• r t
• Inputting and displaying object
• Private functions
• Inspecting and mutating (changing) data members
• Users should not inspect or change num/denom
  directly

8
Class Rational
Public interface Add(), Subtract(),
Multiply(),Divide(), Equal(),
LessThan(), Display(), Get()
Data members NumeratorValue,
DenominatorValue
Private Numerator(), Denominator(),
SetNumerator(), SetDenominator(),
Rational a(1,2)
Rational b(2,3)
b Values
a Values
NumeratorValue(1)
NumeratorValue(2)
DenominatorValue(2)
DenominatorValue(3)
9
main()

• void main()
• Rational r
• Rational s
• cout ltlt "Enter two rationals(a/b) "
• r.Get()
• s.Get()
• Rational t(r) // t r
• Rational sum r.Add(s) // sum r s
• Rational product r.Multiply(s) // product r
  s
• r.Display()
• cout ltlt " "
• s.Display()
• cout ltlt " "
• sum.Display() cout ltlt endl
• r.Display()
• cout ltlt " "
• s.Display()

10
Rational Overview

• class Rational
• public
• // for everybody (e.g. main())
• private
• // for Rational member functions only

11
Rational Public

• public
• // default constructor
• Rational()
• // explicit-value constructor
• Rational(int numer, int denom 1)
• // arithmetic facilitators
• Rational Add(const Rational r) const
• Rational Multiply(const Rational r) const
• // i/o facilitators
• void Display() const
• void Get()

12
Rational Private

• private
• // inspectors
• int Numerator() const
• int Denominator() const
• // mutators
• void SetNumerator(int numer)
• void SetDenominator(int denom)
• // data members
• int NumeratorValue
• int DenominatorValue

13
const

• const Rational OneHalf(1,2)
• OneHalf.Display() // no problem
• OneHalf.Get() // illegal OneHalf is a const

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Default Constructor

• // default constructor
• RationalRational()
• SetNumerator(0)
• SetDenominator(1)
• Example
• Rational r // r 0/1

15
Specific Constructor

• // specific constructor
• RationalRational(int numer, int denom)
• SetNumerator(numer)
• SetDenominator(denom)
• Example
• Rational t(2,3) // t 2/3

16
Inspectors

• int RationalNumerator() const
• return NumeratorValue
• int RationalDenominator() const
• return DenominatorValue
• Where is the following legal?
• int a Numerator()
• Answer In a member function only, because
  Numerator() is private.

Why the const?
17
Mutators

• void RationalSetNumerator(int numer)
• NumeratorValue numer
• Where is the following legal?
• SetNumerator(1)
• Answer In a member function only, because
  SetNumerator() is private.

Why no const?
18
Mutators

• void RationalSetDenominator(int denom)
• if (denom ! 0)
• DenominatorValue denom
• else
• cout ltlt "Illegal denominator " ltlt denom
• ltlt "using 1" ltlt endl
• DenominatorValue 1
• Example
• SetDenominator(5)

19
Facilitators

• Rational RationalAdd(const Rational r) const
• int a Numerator()
• int b Denominator()
• int c r.Numerator()
• int d r.Denominator()
• Rational result(ad bc, bd)
• return result
• Example
• Rational r t.Add(u)

20
Facilitators

• Rational RationalMultiply(const Rational r)
  const
• int a Numerator()
• int b Denominator()
• int c r.Numerator()
• int d r.Denominator()
• Rational result(ac, bd)
• return result
• Example
• Rational r t.Multiply(u)

21
I/O Facilitators

• void RationalDisplay() const
• cout ltlt Numerator() ltlt '/' ltlt Denominator()
• Example
• t.Display()

22
I/O Facilitators

• void RationalGet()
• int numer
• int denom
• char slash
• cin gtgt numer gtgt slash gtgt denom
• SetNumerator(numer)
• SetDenominator(denom)
• Example
• t.Get()