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

• Bitwise operators
• Intro operator overloading
• Quiz 1

• Administrivia
• Use office hours
• Face to face clears things up a lot faster
• Reading
• 8.1 8.7

3
BitvectorRepresentation of Sets

• Integer is a sequence of 32 bits
• dth bit indicates whether d is in the set or not

• Operations
• Add to the set
• Delete from the set
• Check for membership
• Union
• Difference
• Intersection

4
Binary Reping Sets

• int set 0x5A // Binary 0101 1010, decimal 90
• // Integers in the set, 1 3 4 6
• // Technically, can hold 32 integers
• // 0 to 31
• // 0000 0000 0000 0000 0000 0000 0101 1010
• // Another set
• int another_set 0xdecafbad
• // 1101 1110 1100 1010 1111 1011 1010 1101

5
Adding an Element

• int set 0x5A // Binary 0101 1010, decimal 90
• // Adding a an integer d to the set
• // Left shift, bitwise or
• int d 7
• int mask 1 ltlt d
• set set mask
• set mask
• set 1 ltlt d

6
Membership Testing

• int set 0x5A // Binary 0101 1010, decimal 90
• // Testing membership of int d in the set
• // Left shift, bitwise and
• int d 7
• int mask 1 ltlt d
• int test set mask

7
Deleting a Member

• int set 0x5A // Binary 0101 1010, decimal 90
• // Deleting d from the set
• // Left shift, negate, bitwise and
• int d 6
• int mask 1 ltlt d // mask 0100 0000
• mask mask // mask 1011 1111
• int test set mask

8
Set Abstract Datatype

• ifndef _SET_H_
• define _SET_H_ 1
• class BitSet
• public
• BitSet()
• void add(int d)
• void del(int d)
• bool is_member(int d)
• public
• int bits
• endif

9
Set Abstract Datatype

• BitSetBitSet()
• bits 0
• BitSetadd(int d)
• int mask 1 ltlt d
• bits mask

10
Set Abstract Datatype

• BitSetdel()
• int mask 1 ltlt d
• mask mask
• bits mask
• bool BitSetis_member(int d)
• int mask 1 ltlt d
• int test bits mask
• test ? true false

11
Set Abstract Datatype

• include ltctimegt
• include ltcstdlibgt
• include "BitSet.h"
• int main()
• BitSet bit_set
• for(int i 0 i lt 10 i)
• int d rand() 32
• bit_set.add(d)
• return 0

12
Operator Overloading

• Syntactic extension
• Class mechanism
• Let's us add new datatypes
• But dont look like builtins
• Method syntax isn't always natural

13
Set Abstract Datatype

• include ltctimegt
• include ltcstdlibgt
• include "BitSet.h"
• using namespace std
• int main()
• BitSet bit_set
• srand(time(0))
• for(int i 0 i lt 10 i)
• int d rand() 32
• bit_set d // Wouldn't it be nice if

14
Set Abstract Datatype

• // Stuff elided
• include ltiostreamgt
• using namespace std
• int main()
• BitSet bit_set
• // Stuff elided
• // Let's print out a bitset
• cout ltlt "BitSet"
• for (int j 0 j lt 32 j)
• if (bit_set.is_member(j))
• cout ltlt j
• cout ltlt ""
• cout ltlt endl

15
Set Abstract Datatype

• // Stuff elided
• include ltiostreamgt
• using namespace std
• int main()
• BitSet bit_set
• // Stuff elided
• // Let's print out a bitset
• cout ltlt bit_set ltlt endl // Wouldn't it be nice

16
Operator Overloading

• // Stuff elided
• BitSet operator(BitSet bs, int d)
• bs.add(d)
• return bs
• int main()
• BitSet bit_set
• for(int i 0 i lt 10 i)
• int d rand() 32
• bit_set d // Wouldn't it be nice if

17
Operator Overloading

• ifndef _SET_H_
• define _SET_H_ 1
• class BitSet
• public
• BitSet()
• void add(int d)
• void delete(int d)
• bool is_member(int d)
• // Let's hook into C's syntax
• BitSet operator(int d)
• private
• int bits
• endif

18
Operator Overloading

• BitSetBitSet()
• bits 0
• BitSetadd(int d)
• int mask 1 ltlt d
• bits mask
• BitSet BitSetoperator(int d)
• add(d)
• return this

19
Operator Overloading

• // Has to be a standalone function not member
  function
• ostream operatorltlt(ostream os, BitSet bs)
• int foo 10
• cin gtgt foo
• return os
• int main()
• BitSet bit_set
• // Stuff elided
• // Let's print out a bitset
• cout ltlt bit_set ltlt end // Wouldn't it be nice

20
Operator Overloading

• What can be overloaded
• Most operators
• Can't do
• . ., ?
• Can't add any new ones
• Can't change associativity
• Can't change precedence
• Can't change arity
• Nothing done automatically for you
• Issues
• arity binary vs unary
• operator side

• Use cautiously
• Obscures behavior
• Can actually implement opposite behavior for an
  operator

21
Thats a Wrap

• Takeaways
• Bits can represent sets
• Building an ADT on that representation
• Operator overloading
• Syntactic extension

• Reading 8.1 8.7