1 / 15

Announcements

Announcements. Midterm Dates First Midterm Exam: November 22, 2008, Saturday, 10:40 – 12:20 Second Midterm Exam: December 26, 2008, Friday, 17:40 – 19:20 First homework is due on October 1 5 , Wednesday, 19 :00 Submit to SUCourse

thor-slater
Download Presentation

Announcements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Announcements • Midterm Dates • First Midterm Exam: November 22, 2008, Saturday, 10:40 – 12:20 • Second Midterm Exam: December 26, 2008, Friday, 17:40 – 19:20 • First homework is due on October 15, Wednesday, 19:00 • Submit to SUCourse • Strictly follow the submission guideline provided in the homework specification • New (Second) homework will be assigned next week • Email list is active • CS201-AB-200801@sucourse.sabanciuniv.edu • A service provided by SUCourse • Your sabanciuniv accounts must be in this list • We’ve already sent some emails to this list. Did you get them? • We will make announcements to the list and sometimes to SUCourse • Check your emails and SUCourse regularly • Please do not subscribe this list address to some other lists

  2. Chapter 2 – Continued / Functions • Main function • A program is a collection of functions and classes • main and other programmer defined functions • only main is executed automatically when the program starts • other functions must be called to be executed • Programmer-defined functions • piece of code to do a specific job • must be declared before using (this is called calling a function) return-typefunction-name(parameters) { local variables statements } • to execute a function just write its name (and arguments for parameters) • When a function is called, execution order temporarily jumps to function • after the function ends, execution order goes back to the caller • For the time being • return type is void – that means returns nothing • no parameters (we will see parametric functions today)

  3. Why Functions? • Divide and Conquer technique • divide your problem into small ones • write one function for each • combine them in the main program • Provides modularity • when you need to replace a piece of code, you just change a function • you may not need to change the main program • Reuse the same code piece several times • avoid repeating the same code

  4. With no Functions #include <iostream> using namespace std; int main() { cout << " |||||||||||||||| " << endl; cout << " | | " << endl; cout << " | o o | " << endl; cout << " _| |_ " << endl; cout << "|_ _|" << endl; cout << " | |______| | " << endl; cout << " | | " << endl; return 0; } • Prints head, but not so modular • changing the head style requires an update in main. Is this bad? • in this “small” example, need for modularity may not be clear, but in long programs you will need it. • Several heads (like a totem)? • you have to duplicate the same code

  5. With Functions Seeparts.cppfor the entire program #include <iostream> using namespace std; // functions appear here int main() { Hair(); Sides(); Eyes(); Ears(); Smile(); Sides(); return 0; } • Although more complicated, What are advantages of this main over one in which several output statements appear in main? • modularity • changing the heads = changing function(s) • what about eyeglasses? mustache? (let’s do one) • multiple heads (totem poles)? (let’s do one)

  6. Functions with Parameters • Functions are useful, parameterized functions might be more useful • You may need to pass data into a function when you call it • Consider a generic function to calculate the area of any circle and display it • how will the function know the radius? • solution: parameters • function is defined without knowing the value of the radius • value of radius is passed to the function when it is called • parameters are defined similar to variables type name float radius

  7. Area calculation using parameterized function #include <iostream> using namespace std; // area calculation program that employs functions void calculate_area (float radius) { float area; area = 3.14*radius*radius; cout << "The area of a circle with radius " << radius << " is " << area << endl; } int main() { float r; r = 3; calculate_area(r); calculate_area(2.5); calculate_area(r/2); return 0; }

  8. Area calculation using parameterized function #include <iostream> using namespace std; // area calculation program that employs functions void calculate_area (float radius) { float area; area = 3.14*radius*radius; cout << "The area of a circle with radius " << radius << " is " << area << endl; } int main() { float r; r = 3; calculate_area(r); calculate_area(2.5); calculate_area(r/2); return 0; } radius is 3 Output Screen The area of a circle with radius 3 is 28.26

  9. Area calculation using parameterized function #include <iostream> using namespace std; // area calculation program that employs functions void calculate_area (float radius) { float area; area = 3.14*radius*radius; cout << "The area of a circle with radius " << radius << " is " << area << endl; } int main() { float r; r = 3; calculate_area(r); calculate_area(2.5); calculate_area(r/2); return 0; } radius is 2.5 Output Screen The area of a circle with radius 3 is 28.26 The area of a circle with radius 2.5 is 19.625

  10. Area calculation using parameterized function #include <iostream> using namespace std; // area calculation program that employs functions void calculate_area (float radius) { float area; area = 3.14*radius*radius; cout << "The area of a circle with radius " << radius << " is " << area << endl; } int main() { float r; r = 3; calculate_area(r); calculate_area(2.5); calculate_area(r/2); return 0; } radius is 1.5 Output Screen The area of a circle with radius 3 is 28.26 The area of a circle with radius 2.5 is 19.625 The area of a circle with radius 1.5 is 7.065

  11. Functions with Parameters (continued) • Parameters and Arguments • parameter is the generic name used in function • radius in the calculate_area function • argument is the value passed to function while it is called • 2.5 • r (actually current value of r is passed) • r/2 (actually current value of r/2 is passed) • Parameter list provides type and name of the parameters • Argument type must match parameter type • Functions may have multiple parameters • corresponding arguments are separated by commas • in the same order of parameter list • be careful about the type matching • we will see examples later on • Functions may call other functions (have seen in the totem example and will see in the next example)

  12. Functions with Parameters (continued) • Parameters versus Local Variables • Parameters and defined and used locally, but their initial value comes from the caller function via arguments • Local variables are defined and used in the functionlocally • But the initial value does not come from the caller function • While designing your functions, think carefully about local variables and parameters • If you need to pass the initial value from the caller function, then it should be a parameter. • If you won’t pass the initial value, then it should be a local variable. • Example: in calculate_area function • area is a local variable since we do not pass its initial value from main • radius is a parameter since we need to pass its initial value from main • Unnecessary parameters may cause problems and grade reduction (for homework)

  13. Old McDonald’s Farm • Aim is to have a modular program (with functions) to display the song • each verse repeats using a different animal • refrain parts repeat within verses • A partial output (with two animals only) below Old MacDonald had a farm, Ee-igh, Ee-igh, oh! And on his farm he had a cow, Ee-igh, Ee-igh, oh! With a moo moo here And a moo moo there Here a moo, there a moo, everywhere a moo moo Old MacDonald had a farm, Ee-igh, Ee-igh, oh! Old MacDonald had a farm, Ee-igh, Ee-igh, oh! And on his farm he had a cat, Ee-igh, Ee-igh, oh! With a meowmeow here And a meowmeow there Here a oink, there a oink, everywhere a meowmeow Old MacDonald had a farm, Ee-igh, Ee-igh, oh!

  14. Old McDonald’s Farm (Design of Functions) • Which functions do we need? • a function for only “Ee-igh, Ee-igh, oh!” • a function for the refrain (nakarat) • a function for “And on his farm ...” line • animal is parameter • a function for “With a ...”, “And a ...”, “Here a ...” lines • noise of the animal is a parameter • a function for the whole verse • in the main program call the verse function with several animal and noise arguments

  15. Old McDonald’s Farm (Program) • See oldmac2.cpp • Remarks • functions call functions • Refrain calls EiEio • Verse calls Refrain • Verse has two parameters • therefore it is called using two arguments –first one is for animal, second is for noise • order of arguments is important • animal is used as parameter in two functions. • Should we need to use the same parameter name in both cases? Or can we use different names in two different functions? • Same questions are valid for noise as well. • Answer is “Yes we can use different names”. Let’s do and see. • Can we input animal and noise? • of course yes (will do)

More Related