CS 211: Introduction to Computer Programming II

1
CS 211Introduction to Computer Programming II

• Instructor Brian M. Dennis
• Teaching Assistants
• Tom Lechner, Bin Lin, Rachel Goldsborough
• http//www.cs.northwestern.edu/bmd/cs211/

2
Todays Topics

• Destructors
• The delete operator
• setters/getters
• Extended example
• Linked list
• Struct version
• Class version

• Administrivia
• Reading 6.12, 6.13, 6.14, 6.16
• Appendix C if you need it

3
Assignment/delete

• Two ops defined on all classes
• Assignment
• Memberwise bit copy

• Delete
• Calls a no-op destructor
• What's a destructor?

4
C Class Mechanism

• Data abstraction feature
• User defined datatype
• Collection
• Compound data
• Heterogeneous
• Typed fields
• Indexed by name

• Access control
• Information hiding
• Controlled initialization deallocation
• Encapsulation
• data operations on that data

5
Class basics

• // Use overloading to define default constructor
• class MLBPlayer
• public // Access specifier
• MLBPlayer(char name, char team) //
  Constructor
• MLBPlayer() // Default constructor
• // Member functions
• int totalHits()
• float battingAverage()
• void addHit(int hit)
• void strikeout()
• enum Hit SINGLE 0, DOUBLE, TRIPLE, HOMER
  
• private
• // Member variables
• char name char team
• int at_bats int walks
• int hits4
• float batting_average bool bats_lefty

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Class basics

• include "MLBPlayer.h"
• include ltcstringgt
• MLBPlayerMLBPlayer(char n, char t)
• int cnt strlen(n) 1
• name new charcnt
• strcpy(name, n)
• cnt strlen(t) 1
• team new charcnt // fixed up from last
  lecture
• strcpy(team, t)
• at_bats walks 0
• bats_lefty false
• batting_average 0.0
• for (int i 0 I lt 4 i) hitsi 0

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Class basics

• int MLBPlayertotalHits()
• int hits_count 0
• for (int i 0 i lt 4 i)
• hits_count hitsi
• return hits_count
• void MLBPlayeraddHit(int hit)
• at_bats
• if ((SINGLE lt hit) (hit lt HOMER))
• hitshit 1

8
Memberwise copy

• include "MLBPlayer.h"
• include ltcstringgt
• int main(int argc, char argv)
• MLBPlayer cubs_starters9
• cubs_starters0 MLBPlayer("Corey Patterson",
• "Chicago Cubs")
• cubs_starters3 MLBPlayer("Sammy Sosa",
• "Chicago Cubs")
• pinch_hit(8, "Tom Goodwin")

9
Instance deallocation

• // stuff from above
• bool pinch_hit(int pos, char name,
• MLBPlayer lineup)
• MLBPlayer on_deck(name,
  lineuppos.getTeam())
• if (!calledBack(name))
• lineuppos on_deck
• return false
• else
• return true
• // What happens to on_deck here?

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Destructors

• class MLBPlayer
• public
• MLBPlayer(char name, char team)
• MLBPlayer()
• MLBPlayer() // Destructor for the class
• enum Hit SINGLE 0, DOUBLE, TRIPLE, HOMER
  int totalHits()
• float battingAverage()
• void addHit(int hit)
• void strikeout()
• private
• char name char team
• int at_bats int walks int hits4
• float batting_average
• bool bats_lefty

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Destructors

• // Defining the (and only) constructor
• // for a class
• MLBPlayerMLBPlayer()
• delete team // Give back space for team
• delete name // Give back space for name
• // Except now we have another problem!!

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Destructors

• // stuff from above
• bool pinch_hit(int pos, char name,
• MLBPlayer lineup)
• MLBPlayer on_deck(name,
  lineuppos.getTeam())
• if (!calledBack(name))
• lineuppos on_deck // But we member copied!
• return false
• else
• return true
• // On deck gets cleaned up!

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Some delete examples

• include "MLBPlayer.h"
• include ltcstringgt
• int main(int argc, char argv)
• MLBPlayer cubs_starters9
• MLBPlayer leadoff_hitter cubs_starters0
• MLBPlayer closer new MLBPlayer("Eric Gagne",
• "LA Dodgers")
• MLBPlayers dodgers new MLBPlayers9
• delete cubs_starters
• delete cubs_starters
• delete leadoff_hitter
• delete closer
• delete dodgers
• delete dodgers

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Constructor/destructor exec

• include "MLBPlayer.h"
• MLBPlayer ichiro("Ichiro", "Seattle Mariners")
• int main(int argc, char argv)
• MLBPlayer cubs_starters9
• MLBPlayer local_player
• on_injured_reserve(local_player)
• MLBPlayer dynamic_player new MLBPlayer
• MLBPlayer big_unit("Randy Johnson",
  "Diamondbacks")
• return 0
• void on_injured_reserve(MLBPlayer p)
• static cnt 0
• static MLBPlayer reserve4
• reservecnt p
• cnt

15
Linked list example

• Time permitting

16
Thats a Wrap

• Takeaways
• Memberwise copy
• Instance allocation deallocation
• Setters and getters