lecture9

lecture9 - Wednesday Febr uar y 5 th Custom Compar i son...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Wednesday, February 5 th Custom Comparison Operators Templates The Standard Template Library (STL) STL Iterators STL Algorithms (find and find_if)
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Recursion Challenge The following function iteratively computes x n : int exponentiate(int x, int n) { int i, result = 1; for(i=0; i<n; i++) result *= x; return result; } Write a function to do this recursively.
Background image of page 2
Custom Comparison Operators Consider the following main function that compares various objects to each other… Notice that the way we compare two dogs (by weight) is different than the way we compare two circles (by radius) . main() { int i1 = 3, i2 = 5; if (i1 > i2) cout << “i1 is bigger”; Circ a(5), b(6); if (a. radius () > b. radius ()) cout << “a was bigger”; Dog fido(10), spot(20); if (fido. weight () > spot. weight ()) cout << “fido is bigger”; } Wouldn’t it be nice if we could compare objects like circles and dogs just like we compare two integers? if (a > b) if (fido > spot) cout << “fido is bigger”; We can! Let’s see how!
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The way to solve this is to define a comparison function for each data type… bool operator > (const Dog &a, const Dog &b) { if (a. weight () > b. weight ()) return(true); else return(false); } bool operator > (const Circ &a,const Circ &b) { if (a. radius () > b. return(true); else return(false); } Once defined, you can use the operator in your program! Dog fido(5), spot(3); if (fido > spot) cout << “fido wins”; Circ c(3), d(2); if (c > d) cout << “c is bigger”; } Custom Comparison Operators And of course, you can define your own versions of other comparison operators too… bool operator == (const Dog &a, const Dog &b) { if (a. weight () == b. weight ()) return(true); else return(false); } bool operator != (const Dog &a, const Dog &b) { if (a. weight () != b. weight ()) return(true); else return(false); } bool operator >= (const Dog &a, const Dog &b) { if (a. weight () >= b. weight ()) return(true); else return(false); } = spot weight 3 Simply using the >= operator causes C++ to call your comparison function! 5 3 All comparison operators must return a Boolean value: true or false All comparison operators accept two const reference parameters. These refer to the two objects being compared. (While making them const isn’t always required, leaving it out can cause compiler errors!) Carey says: Similarly, Dog’s weight() function must be const. class Circ { public: int radius() const { return(m_rad); } ... private: int m_x,m_y,m_rad; }; Carey says: Oh, and by the way… since a and b are const, Circ’s radius() now needs to be const too or else you’ll get an error!
Background image of page 4
Templates In this code, we’ve written several different swap functions that swap the two values passed into the function. // the old way void SwapCircle (Circ &a, Circ &b) { Circle temp; temp = a; a = b; b = temp; } void SwapDog (Dog &d1, Dog &d2) { Dog temp; temp = a; a = b; b = temp; } main() { Circle a(5), b(6); Dog c(100), d(750); SwapCircle (a,b); SwapDog (c,d); } Wouldn’t it be nice if we could write one swap function and have it work for any data type?
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/07/2009 for the course CS 32 taught by Professor Davidsmallberg during the Winter '08 term at UCLA.

Page1 / 46

lecture9 - Wednesday Febr uar y 5 th Custom Compar i son...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online