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Fondamenti della Programmazione: Metodi Evoluti Prof. Enrico Nardelli
Lezione 1: Introduction
versione originale: http://touch.ethz.ch
Obiettivi formativi
• Padroneggiare la programmazione in modo professionale.
• Chiunque può scrivere programmi funzionanti • Non ci si sporca, né si suda • Scrivere programmi funzionanti in modo robusto
ed affidabile, anche e soprattutto man mano che li si modifica ed aggiorna, richiede strumenti e tecniche adeguate.
• Cosa usiamo nel corso: • il linguaggio orientato agli oggetti Eiffel • la metodologia di progetto Design by Contract • l'approccio outside-in allo sviluppo di programmi
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Schedule
Lezioni: Martedi, 9:00 – 11:00, Aula L3 Venerdi, 9:00 – 11:00, Aula L3
Spiegazioni: Al termine delle lezioni Su richiesta, previo appuntamento per e-mail
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About me
Contact: E-mail: nardelli@mat.uniroma2.it Telephone: 06 7259 4204 Office: 0123, piano terra, dente 1, Dipartimento di Matematica
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Course web page (in italiano): http://www.mat.uniroma2.it/nardelli/fondamenti-programmazione-metodi-evoluti.html
Informazioni organizzative Materiale didattico: Informazioni e risultati esami Ricevimento studenti
The original page (in english): http://se.inf.ethz.ch/old/teaching/2009-H/eprog-0021/english_index.html
Lecture slides (link: slides and video recordings) • Also audio/video recording of original lectures by B.Meyer
Exercise material • Text and solutions • Supplementary slides
Advanced topics
Course information
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Dalla mia pagina web del corso
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The textbook
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The software
The exercises rely on: the EiffelStudio “development environment” the Traffic “library” Application domain: Transportation system in a city (Paris is used as an example) You will need to download:
EiffelStudio: http://dev.eiffel.com/ Traffic: http://traffic.origo.ethz.ch/download
(see instructions on exercise sheet of week 1). It’s useful to have a PC…
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Discovering Traffic
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Warning
Not everything is perfect... The software probably has mistakes (“bugs”), and the textbook does, too… BUT:
Mistakes will be corrected, as quickly as possible. If you try something, don’t blame the software
first. It may be doing just what you told it to.
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Why this approach?
• Many software issues become really tough for big systems
• With other approaches, in a fundamentals course, you only see small programs
• Here you get lots of software; use it as model & inspiration
• You learn to use software through abstract interfaces (also known as contracts)
• You go from consumer to producer: outside-in • Traffic is graphical and fun! • You should at the end be able to understand all of it. • Then you can add to it yourself
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Basic advice
Attend all lectures Read material — textbook, slides — before lecture Bring a printout of the slides to the lecture, take notes Attend all exercise sessions Do all exercises If you don’t understand, ask
(again: there are no stupid questions) Don’t prepare for the exam at the last minute Keep a critical, probing attitude
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Previous programming experience
If you have already programmed, take advantage of it, but using a fresh look; explore Traffic If you are new to programming, don’t be afraid; it can be hard at the beginning but you’ll get the hang of it. Mathematics is as useful a preparation as programming experience
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THE INDUSTRY OF PURE IDEAS
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Topics
What is software? Objects & programs Interfaces and the notion of class Logic and contracts The run-time model: object creation, references Describing syntax Control structures
Inheritance Genericity Recursion Data structures Event-driven programming & agents Topological sort Intro to software engineering
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Software engineers build machines
• You can’t touch, kick or drop our machines: they’re immaterial
• But they are machines anyway • We call them programs or systems
• To operate (or run or execute) a program you
need a physical machine: a computer
• Computers and related devices: hardware
• Programs and associated intellectual value: software
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Software everywhere
• Banking: manage millions of accounts • Trading: decide to sell or buy • Transportation: control trains, track planes...
Some cars have millions of lines of program code • Travel: air, train, hotel reservations • Communication: phones, Internet, … • Government: manage taxes, track laws... • Health care: keep health record, control devices • Education • Entertainment • Information • etc.
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Computers everywhere
Banks Airplanes, cars… Washing machines Cell phones (70% of value) Printers Tomorrow: your shirt…
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Computers come in all sizes, colors, flavors
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Computers
Computers are universal machines. They execute the program that you feed them
The only limit is your imagination
The good news:
Your computer will do exactly what your program says
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Building and running programs
Programmer: writes programs User: runs programs
A programmer writes a
a user
which
runs on
a computer
Program
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Program using
a computer A programmer
which
runs on
a computer
writes a
a user
Building and running programs
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users
their computers
using a computer
run on
which
Program
Building and running programs
writes a
A programmer
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Programmers
which
their computers
using computers
run on
Program
users
Building and running programs
write a
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Computers
Computers are universal machines. They execute the program that you feed them.
The only limit is your imagination.
The good news:
Your computer will do exactly what your program says.
It will do it very fast.
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Moore’s “Law”
Approximate doubling of computing power, for comparable price, every eighteen months (Is this what Moore’s law says?) (No: approximate doubling of the number of transistors)
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Moore’s law (source: Intel)
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Moore’s “Law”
Approximate doubling of computer power, for comparable price, every eighteen months
2000
1 MHz
10 MHz
1 GHz
100 MHz
1990 1980 1970
8008: < 1 MHz
80386: 33 MHz 80486: 50 MHz
Pentium: 133 MHz
Pentium IV: 1.3 GHz
to 1 GHz: 26 years from 1 to 2 GHz: 8 months
Speed of Intel processors
(1 Hertz = 1 clock cycle per second)
3.8 GHz
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Microprocessors (source: Intel)
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Common myths and excuses
“Computers are intelligent” Fact: Computers are neither intelligent nor stupid.
They execute programs devised by humans. These programs reflect the intelligence of their authors.
The basic computer operations are extremely elementary (store this value, add these two numbers…).
“The computer has crashed” “The computer doesn’t allow this” “The computer lost your record” “The computer messed up your record”
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Computers don’t make mistakes *....
Programs don’t make mistakes either Programmers do make mistakes
*Actually, hardware can malfunction, but this is much more rare than program errors
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Computers
Computers are universal machines. They execute the program that you feed them
The only limit is your imagination
The good news:
Your computer will do exactly what your program says
It will do it very fast
The bad news:
Your computer will do exactly what your program says
It will do it very fast
“To err is human, but to really mess
things up takes a computer”
and your carefulness
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The “Blue Screen Of Death”
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Writing software is tough
• Programs “crash” • Programs that don’t crash don’t necessarily work • Incorrect programs have killed people, e.g. in
medical devices
• Programmers are responsible for the correct functioning of their programs
• The purpose of this course is to teach you not just programming but good programming
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Learning to program well
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An highly expensive software error
Look at the consequences of a program error! http://www.youtube.com/watch?v=kYUrqdUyEpI Ariane 5 rocket, 1996: 370 million US$ lost because of a simple program error (7 billion US$ is the total cost of the rocket development) Jean-Marc Jézéquel & Bertrand Meyer: Design by
Contract: The Lessons of Ariane, in Computer (IEEE), vol. 30, no. 1, January 1997, pages 129-130, archive.eiffel.com/doc/manuals/technology/contract/ariane/.
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Worst software failures
10 worst software bugs (until 2005): http://www.wired.com/software/coolapps/news/2005/11/69355?currentPage=all A more recent account http://www.computerworld.com/s/article/9183580/Epic_failures_11_infamous_software_bugs 10 worst software failures in 2011 http://www.testmagazine.co.uk/2011/12/top-ten-worst-software-failures-of-2011/ 10 worst software failures in 2012 http://www.testmagazine.co.uk/2012/12/the-highest-profile-software-failures-of-2012/ 1-INTRODUZIONE Rev. 1.1.5 (2015-16) by Enrico Nardelli from B.Meyer's originals 37
What computers do
Memories, processors and communication devices are the hardware
Rest of the world
Processors
Memories
Communication
devices
Storage and retrieval Memories
Operations Processors
Communication Communication devices
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General organization
Rest of the world
Processors
Memories
Communication
devices
“Core” memory, disks...
“Persistent” or not
Keyboard, mouse, video display, network connector...
Also “CPU”
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Computers
Computers are universal machines. They execute the program that you feed them.
Program
(Universal machine)
+ = Specialized
machine
Software
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•Data: collections of symbols held in a computer • Information: interpretation of data for human purposes
Information and data
Information is what you want, e.g. a text or music Data is how it is encoded for the computer, e.g. MP3 audio format
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Information and data processing
Data is stored in memory Input devices produce data from information Output devices produce information from data Information Information
Data
Data
Data Input Output
Process
Computer
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Where’s the program?
Stored-program computer: the program is in memory “Executable data”
A program can appear in memory in different forms:
Source: human-readable form (programming language) Target form, machine code, object form: form executable
by the computer A compiler transforms source text to machine code The computer (more precisely the platform: computer + operating system) finds your program in memory to execute it
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Software Engineering
Writing software that’s Correct
Does what it’s supposed to! Extendible
Easy to change! Readable
by humans! Reusable
Don’t reinvent the wheel! Robust
React appropriately to errors Secure
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Operating systems: source size
Unix V7: 10K
1990 1992
1995 1998 2000
Red Hat 7.1: 30
Linux: 10 K
10
20
40
30
Lines of code (millions)
Windows 3.1: 3 M Windows NT: 4 M
Windows 95: 15 Windows 98: 18
Windows 2000: 40
Red Hat 6.2: 17 Solaris 7: 12
Windows XP: 45
2006
50 Vista: 50
Debian 2.2: 55
Debian 3.1: 213!
2001
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Writing software is tough
It is difficult to get a program right Trial-and-error approach very inefficient
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Writing software is fun
Design and build your own machines Exert your creativity and imagination Programs save lives and help make the world better Experience the feeling of a program that you wrote, and that works
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