Chair of Software Engineering 1 Introduction to Programming Bertrand Meyer Exercise Session 2 23 September 2008

Chair of Software Engineering 2 Organizational  Assignments  One assignment per week  Will be put online on Friday (download it from the web site) ‏  Will be due on Thursday the next week  (Assignment 1 was an exception) ‏  Asking questions  Exercise sessions  /come to my office  Group mailing list  Is everybody subscribed?

Chair of Software Engineering 3 Today Purpose of the exercise session:  Give you the intuition behind object-oriented (OO) programming  Teach you about formatting your code  Get rolling with EiffelStudio & Traffic (Assignment 1)

Chair of Software Engineering Objects and classes  Classes are pieces of software code  One or several classes can make up a program  Objects are instances of classes  Classes define operations applicable to their instances Example: A class STUDENT can define operations applicable to all its instances, such as subscribing to a course, registering for an exam, etc. This means that all class STUDENT’s instances (such as the students Bob, Mike, Steve, etc.) will be able to subscribe themselves to a course, to register for an exam, etc.  Only operations defined in a class can be applied to its instances

Chair of Software Engineering 5 Calling a feature on an object (1)  next_message  send  computer  shut_down  telephone  ring Every operation applies to an object and may take arguments

Chair of Software Engineering 6 Calling a feature on an object (2)  next_message  send_to (recipient) ‏  computer  shut_down_after (3) ‏  telephone  ring_several (10, Loud) ‏ Every operation applies to an object and may take arguments

Chair of Software Engineering 7 Exercise: class BANK_ACCOUNT  Class BANK_ACCOUNT defines and implements the following operations:  deposit (i: INTEGER)  withdraw (i: INTEGER)  close  If b: BANK_ACCOUNT (b is an instance of class BANK_ACCOUNT) which of the following feature calls are possible:  b.deposit (10)  b.deposit  b.close  b.close (“Now”)  b.open  b.withdraw (100.50)  b.withdraw (0) Hands-On

Chair of Software Engineering 8 class PREVIEW inherit TOURISM feature explore is -- Show city info and route. do “To be filled in (by you!)” end A class text Softwar e machine Extend an existing class Operations Featur e name Commen t Keywords have a special meaning: class, inherit, feature, is, do, end. Feature declaratio n Pseudocod e

Chair of Software Engineering 9 Da style rules!  For indentation, use tabs, not spaces  Use this property to highlight the structure of the program, particularly through indentation CLASS NAMES: ALL UPPERCASE Period in feature call: no space before or after

Chair of Software Engineering 10 Exercise: format class bank_account feature deposit (sum: INTEGER) is -- Add `sum' to the account. do balance := balance + sum end balance: INTEGER end Hands-On

Chair of Software Engineering 11 Solution: format class BANK_ACCOUNT feature deposit (sum: INTEGER) is -- Add `sum' to the account. do balance := balance + sum end balance: INTEGER end Hands-On

Chair of Software Engineering Assignment 1 Take the remaining time to work on Assignment 1. Try to solve the tasks on your own. Ask me if you have any problems. (We’ll have such a session every week for each assignment.)