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

• Introduction to classes
• Class declaration
• Instance creation
• Members
• Constructors
• Some mopup
• Dynamic allocation
• Binary numbers

• Next week's schedule
• Lecture
• Monday Tuesday
• Wednesday
• Quiz 1
• Friday
• Quiz 1 back hopefully
• Reading
• 6.5 6.10

3
Issues with structs

• Initialization
• Not guaranteed
• Done by hand
• Packaging datatypes behavior
• Connecting

• Reuse / extension
• Salaried players

4
Basics of classes

• // An example of declaring
• // a new user defined type, using the class mech
• class MLBPlayer
• public
• MLBPlayer(char name, char team)
• private
• enum Hit SINGLE 0, DOUBLE, TRIPLE, HOMER
• char name
• char team
• int at_bats
• int walks
• int hits4
• float batting_average
• bool bats_lefty

5
Basics of classes

• 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
• strcpy(team, t)
• at_bats walks 0
• bats_lefty false
• batting_average 0.0
• for (int i 0 I lt 4 i) hitsi 0

6
Basics of classes

• // Moving some private fields to public for
  convenience
• class MLBPlayer
• public
• MLBPlayer(char name, char team)
• int at_bats
• int walks
• float batting_average
• private
• enum Hit SINGLE 0, DOUBLE, TRIPLE, HOMER
• char name
• char team
• int hits4
• bool bats_lefty

7
Basics of classes

• include ltiostreamgt
• using namespace std
• include "MLBPlayer.h"
• // Accessing public member variables
• int main(int argc, char argv)
• MLBPlayer sammy_sosa("Sammy Sosa", "Chicago
  Cubs")
• MLBPlayer bmd_wishes sammy_sosa
• sammy_sosa.at_bats 1
• int total_hits 0
• for (int i 0 i lt 4 i)
• total_hits sammy_sosa.hitsi
• bmd_wishes-gtbatting_average
• total_hits / bmd_wishes-gtat_bats
• return 0

8
Basics of classes

• // Instead of public fields, let's write public
  accessor funcs
• class MLBPlayer
• public
• MLBPlayer(char name, char team)
• 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

9
Basics of classes

• 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

10
Basics of classes

• float MLBPlayerbattingAverage()
• return totalHits() / (at_bats 1.0f)
• void MLBPlayerstrikeout()
• at_bats

11
Basics of classes

• include ltiostreamgt
• using namespace std
• include "MLBPlayer.h"
• // Now using public accessor functions
• int main(int argc, char argv)
• MLBPlayer sammy_sosa("Sammy Sosa", "Chicago
  Cubs")
• MLBPlayer bmd_wishes sammy_sosa
• sammy_sosa.addHit(MLBPlayerSINGLE)
• sammy_sosa.strikeout()
• sammy_sosa.strikeout()
• float ba sammy_sosa.battingAverage()
• return 0

12
Basics of classes

• include ltiostreamgt
• using namespace std
• include "MLBPlayer.h"
• // Now using public accessor functions
• int main(int argc, char argv)
• MLBPlayer sammy_sosa("Sammy Sosa", "Chicago
  Cubs")
• MLBPlayer bmd_wishes sammy_sosa
• bmd_wishes-gtaddHit(MLBPlayerSINGLE)
• bmd_wishes-gtstrikeout()
• bmd_wishes-gtstrikeout()
• float ba bmd_wishes-gtbattingAverage()
• return 0

13
Basics of classes

• // Use overloading to define default constructor
• class MLBPlayer
• public
• MLBPlayer(char name, char team)
• MLBPlayer()
• 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

14
Basics of classes

• include "MLBPlayer.h"
• // Stuff elided
• MLBPlayerMLBPlayer()
• char n "Joe Schlabotnik"
• char t "Waffletown Syrups"
• int cnt strlen(n) 1
• name new charcnt
• strcpy(name, n)
• cnt strlen(t) 1
• strcpy(team, t)
• at_bats walks 0
• bats_lefty false
• batting_average 0.0
• for (int i 0 i lt 4 i) hitsi 0

15
Basics of classes

• include ltiostreamgt
• using namespace std
• include "MLBPlayer.h"
• int main(int argc, char argv)
• // Imagine all our old stuff here.
• MLBPlayer black_sox9
• MLBPlayer joe_s new MLBPlayer
• joe_s new MLBPlayer()
• joe_s new MLBPlayer("Joe Schlabotnik",
  "Waffletown Syrups")
• return 0

16
Dynamic allocation

• include ltcstringgt
• // Leaves us with a dangling pointer, also wastes
  space
• char dup_string(char s)
• const int max_buf 1024
• char bufmax_buf
• strcpy(buf, s)
• return buf
• // Using dynamic allocation we're okay
• char dup_string(char s)
• int cnt strlen(s) 1
• char new_string new charcnt
• return new_string

17
Thats a Wrap

• Take away
• Classes are an improved form of structs
• Know how to declare classes, define member
  functions
• Dynamic allocation
• Space managed by program at run time
• Binary representations