More Classes

1
More Classes
2
IEEE Student Conference

• Student Professional Awareness Conference
• Paul Kostek career options for 21st Century
• Panel discussion by local companies
• April 4, 2002
• Lookout room in SUB
• email to Ben Millemon ieee_at_boisestate.edu
• posters in MEC and ET buildings

3
4/1/02

• exam 3 on April 10
• files
• arrays
• strings
• classes

4
Random numbers

• use the rand function from stdlib.h
• int rand() returns an integer from 0 to RAND_MAX
  (a big number)
• the sequence you get is always the same
• use to get numbers from 1 to 6
• dieValue 1 rand() 6
• randomize.h

5
User Defined Types

• Define what data we want in the class
• what data is needed to represent the class
• Create the functionality to operate on the data
• class member functions provide access to data and
  operations that can be done on or with it

6
Money Class

• Two attributes
• dollars
• cents
• Behavior
• decimal value
• addition
• comparison
• input/output

7
Money.h

• class Money
• public
• Money() dollars cents 0
• Money( double)
• double decValue() const
• private
• int dollars, cents
• // overloaded operators

8
Money Class

• Allocate a Money object
• money unitPrice( 5000.00)
• Assignments
• taxAmount salePrice taxPercent/100.0
• itemPrice unitPrice quantity
• finalCost itemPrice taxAmount

9
Objects and Functions

• class types can be used as both parameters and
  return types for functions
• use C ob1 to pass by value
• a copy is made (copy constructor)
• not efficient for big objects
• Use C ob1 as formal reference argument
• Use const C ob1 to specify object cant be
  modified by a function

10
Objects as Operands

• Assignment operator has a default definition
• ob2 ob1
• Others must be "overloaded"
• gtgt for input
• ltlt for output
• arithmetic if appropriate
• comparison

11
Object Input and Output

• Often need to be able to
• read information to initialize an object
• print out information about an object
• Reading/Printing the information from your
  program or another class is contrary to the goal
  of encapsulation
• Define functions for input and output in the class

12
Approaches

• Write member functions for each operator needed
• read(), print(), equals(), lessThan(), ...
• Overload the appropriate operators
• consistency with primitive variables

13
Class functions

• two approaches
• a.lessThan (b)
• A and b are objects that are compared by passing
  one object to the other objects member function
  lessThan
• lessThan2 (a, b)
• Both objects are treated the same
• Must use a friend function to do this

14
Two ways to write less than

• bool Money lessThan (const Money m) const
• return (decValue()ltm.decValue())
• bool lessThan2 (const Money m1, const Money m2)
• return (m1.decValue() lt m2. decValue())

15
Friends

• Second version of lessThan needs access to the
  private data of the class
• but it isn't a member function so
• Make it a friend function
• declared in the class declaration
• allows access to private data
• example getline for strings
• classes can be friends too

16
Friend Function Declaration

• Form (in class declaration)
• friend result-type function-name (arg list)
• friend result-type operator opSymbol (arg list)
• Example
• friend bool equals (const Money , const Money
  )
• friend bool operator (const Money , const
  Money )

17
Overloading Operators

• lets you use objects the way you do primitive
  types
• can be either member or friend functions
• prototypes are relatively fixed

18
string class

• string s1, s2 " a string", s3
• can use ltlt to print cout ltlt s2
• can use gtgt to read cin gtgt s1
• can use to concatenate s1 s2
• can use to assign s3 "stuff"
• can use , lt, etc. to compare

19
operatorlt

• bool Money operatorlt(const Money m) const
• return (decValue()ltm.decValue())
• bool operatorlt (const Money m1, const Money m2)
• return (m1.decValue() lt m2.decValue())

20
Operators for Money Class

• want input and output
• do it once so you don't have to write it again
  every time you use the class
• addition makes sense for Money objects
• multiply by either a double or an int

21
Common Programming Errors

• Function argument return value errors
• Not defining a function as a member of a class
• Prefixing a class function call
• obj.function()
• Referencing a private attribute of a class
• Missing header files
• Missing on class definition