1. Introduction. 27. Juni 2011

Transcription

1 27. Juni 2011 Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 1 of 41

2 Outline The Course The Motivation The Introduction What is a computer? von-neuman architecture What is a high-level language? bytecode, intermediate languages, and the real world Where does it all come from? historic overview & the software crisis The Development Workflow: Algorithms, Tools, and Activities Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 2 of 41

3 1.1. The Course There ain t no such thing as a free lunch. R. A. Heinlein, The Moon Is a Harsh Mistress Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 3 of 41

4 The Course The Course The Motivation The Speaker Introduction Development Workflow 1.2. The Course Concept Through C/C++ in a rush Programming means training course can t replace it Provide a deeper understanding of underlying mechanisms Three slots a 45 minutes per day Provide some exercises throughout the course lectures Provide some programming support Einfu hrung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 4 of 41

5 Didactic Concept In theory there is no difference between theory and practice. In practice there is. Yogi Berra Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 5 of 41

6 The Course The Course The Motivation The Speaker Introduction Development Workflow After the Course Through C/C++ in a rush Programming means training course can t replace it Provide a deeper understanding of underlying mechanisms Content is tailored to Ph.D. students (not undergrads) Content is aligned with scientific software Three slots a 45 minutes per day Provide some exercises Provide some programming support Temple Church, London Einfu hrung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 6 of 41

7 Calendar From Monday, June 26, till Friday, July 8. Each day three sessions a 45 minutes. We start at 9:30 and end around 12:15. I provide additional programming support each day after the lectures. If I don t stay at the lecture room after the course for the programming support, feel free to write me an (tobias.weinzierl@mytum.de). Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 7 of 41

8 The Guttenberg Slide Martin Fowler: Refactoring Erich Gamma, Richard Helm, Ralph Johnson, John M. Vlissides. Design Patterns: Elements of Reusable Software Randall Hyde: Write Great Code I: Understanding the machine Randall Hyde: Write Great Code II: Thinking Low-level, Writing High-level Scott Meyers. Effective C++ Scott Meyers. More Effective C++ Walter Savitch. Absolute C++ Bjarne Stroustrup. The C++ Programming Language Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 8 of 41

9 1.3. The Motivation... about the Leaning Tower Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 9 of 41

10 The two pillars of science Theory Experiment What happens if these pillars can t be realised or should not be realised? Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 10 of 41

11 The three pillars of science Theory Simulation Experiment Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 11 of 41

12 The Scientific Workflow an Iterative Scheme Numerical Experiments Postprocessing Modelling Numerical Treatment Design of Software Visualisation Tests Implementation Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 12 of 41

13 Scientific Software Crisis PITAC report 2005: Today s CSE ecosystem is unbalanced, with a software base that is inadequate to keep pace with and support evolving hardware and application needs. PITAC report 2005 It is consequently of uttermost importance to have skilled and trained programmers. Programming comprises both a craft and an art, and, hence, coding is not just an unimportant task which can be left to less intelligent henchmen. Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 13 of 41

14 However... PITAC report 2005: Today s CSE ecosystem is unbalanced, with a software base that is inadequate to keep pace with and support evolving hardware and application needs. It is consequently of uttermost importance to have skilled and trained programmers. Programming comprises both a craft and an art, and, hence, coding is not just an unimportant task which can be left to less intelligent henchmen. Almost everybody almost all the time: I agree but in my case it s different. I have better/more urgent things to do than to think about software as, before, I have to understand the underlying physical/technological/medical principles. Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 14 of 41

15 A Success Story Sorry About the Sarcasm Nature 447: In 2006, data from the array led a team of scientists to the surprising conclusion that the world s oceans had cooled during 2003 exceptionally warm years in terms of global surface temperature. The team published its findings in Geophysical Research Letters[1]. Such apparent cooling was seized on by people keen to highlight the uncertainties in forecasts of global warming[2]. That cooling has now been shown to be an artifact. In some of the buoys they are manufactured in separate batches a software glitch caused the temperature and salinity data to be associated with the wrong depths. When the problem data are excluded from the analysis, the cooling trend drops below the level of statistical significance. (pp. 7140) Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 15 of 41

16 Why Matlab sometimes doesn t work Herb Sutter. The free lunch is over: A fundamental turn toward concurrency in software, Dr. Dobb s Journal, 30(3), Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 16 of 41

17 Statements More and more insight will stem from simulations. New insight requires more computing power. More computing power will result from parallelism and other hardware stuff. Mathematicians, engineers, physicians, etc. will write the applications the computer guys write web apps and earn tons of bucks with Google & Co. If you wanna use a tool, you have to learn how to handle it. So learn C/C++/FORTRAN, and, more important, understand what s happening there. Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 17 of 41

18 1.4. The Speaker Excerpt From my CV June 2000-October 2000 October 2000 October 2005 July 2009 October 2009 now July 2011 Work sd&m AG, Munich: Stock exchange (C++) Computer Science at TUM worked at sd&m AG, Munich: Financial services (Java) Hiwi at Chair of Systems & Software Engineering: Übungen zur Einführung in die Informatik (Java) Ph.D. Defense A Framework for Parallel PDE Solvers on Multiscale Adaptive Cartesian Grids (C++) KAUST-TUM Scientific Project Manager Peano framework Software Engineering, coding best practices, and domain-specific languages in High Performance Computing Habil at TUM Lots of HPC software... Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 18 of 41

19 1.5. Introduction A Turing Machine ALU IO Memory If we wanna handle a car/machine (efficiently), we have to know how it works. That doesn t mean that we have to be able to construct a car/machine ourselves. Computer (von-neumann architecture): ALU, Memory, IO Controller, Bus Processor (Very) simple binary operations such as add, increment,... Takes one or two numbers, combines them, and writes back result to memory Has a program counter holding one number Memory Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 19 of 41

20 Memory Processor ALU 21: 22; Memory (Very) simple binary operations such as add, increment,... Takes one or two numbers, combines them, and writes back result to memory Has a program counter holding one number IO 23; 24; 4 25; 5 26; 27; 28: Memory Long linear sequence of post its (storage locations) Sequence of storage locations holds natural numbers Storage locations are enumerated Example: Add entry 24 and entry 25 and write result back to entry 21 Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 20 of 41

21 A First Machine Code Processor ALU 21: 22; Memory (Very) simple binary operations such as add, increment,... Takes one or two numbers, combines them, and writes back result to memory Has a program counter holding one number IO 23; 24; 4 25; 5 26; 27; 28: Memory Long linear sequence of post its (storage locations) Sequence of storage locations holds natural numbers Storage locations are enumerated Example: Add entry 24 and entry 25 and write result back to entry 21 Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 21 of 41

22 Program Counter Processor PC: 113 ALU Memory 21: 22; 23; 24; 4 25; 5 26; 27; 28: 113: add 114; ; ; 21 (Very) simple binary operations such as add, increment,... Takes one or two numbers, combines them, and writes back result to memory Has a program counter holding one number Memory Computer program is a sequence of natural numbers Each number equals command (code) Program counter tells ALU which command to execute next Program counter incremented after each command Random access memory machine RAM machine Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 22 of 41

23 Instruction Streams PC: 113 ALU 21: 22; 23; 24; 4 25; 5 26; 27; 28: Memory 113: add 114; ; ; 21 Properties of machine instructions Code, i.e. number-to-command mapping, is machine-specific Set of available commands is machine-specific Constraints on codes (which codes are allowed when) are machine-specific Performance of a command is machine-specific Writing machine code Cumbersome (small number of directives) Error-prone Not portable We need a more abstract program description (programming language). Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 23 of 41

24 Algorithm An algorithm is a method/recipe expressed as finite list of effective instructions/actions for calculating a function/solving a problem. Where do we find algorithms on a daily basis? Abu Abdullah Muhammad bin Musa al-khwarizmi Persian mathematician, A.D. Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 24 of 41

25 Cooking Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 25 of 41

26 Cooking by Isaac Nassi and Ben Shneiderman Open Door of Appartment All guys enter room Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 26 of 41

27 Cooking by Isaac Nassi and Ben Shneiderman Open Door of Appartment All guys enter room Hungry? Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 27 of 41

28 Cooking by Isaac Nassi and Ben Shneiderman Open Door of Appartment All guys enter room No Hungry? Yes Call Pizza service Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 28 of 41

29 Cooking by Isaac Nassi and Ben Shneiderman Open Door of Appartment All guys enter room No Hungry? Yes For each buddy Open a beer Call Pizza service Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 29 of 41

30 Create your own diagram Write down a Nassi Shneiderman diagram (belonging to structured programming) for the following formula: s(n) = k k with n mod k = 0. Hint: Just run over all k and find out whether they fit into n. Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 30 of 41

31 Translation Concepts Algorithm Compiler (Translator) Compiler (Translator) To be done once Machine Code To be done for each architecture Sell/give it to the customer Install it on the computer Intermediate Code Sell/give it to the customer Install it on the computer Interpreter (Simultan Translator) Machine Code Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 31 of 41

32 A Compiler is a big translation table, i.e. a = 4; b = 5; c = a + b becomes move 4 to 24 move 5 to 25 add to does all the management and linearisation of the memory stream... provides more abstract commands than the machine language can do... manages the program counter... and does a lot more Each real computer scientist has to invent at least one new language and write the corresponding compiler once in his/her lifetime! Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 32 of 41

33 History of C Origins (1970s) Zoo of languages & compilers Among them A and B (Ken Thompson, invented UNIX) Use to write operating systems History of C 1972, Dennis M. Ritchie, Bell Laboratories, AT&T 1973/74, Brian W. Kernighan Purpose: Write operating systems and compilers Fundamental concepts of C Powerful to write an operation system Small number of commands Structuredness (no sequences of assembler code) State of C Used to write UNIX General purpose language Available on all UNIX systems Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 33 of 41

34 History of C++ Bjarne Stroustrup Software Crisis (80s) Complex systems, difficult to maintain Lack of abstraction Lack of modelling facilities Smalltalk and the OOP History of C++ early 80s, Bjarne Stroustrup, Bell Laboratories, AT&T extension of C, i.e. C programs are C++ programs with new ideas of OOP Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 34 of 41

35 C++ State of the Art? PC: 113 ALU Memory 21: 22; 23; 24; 4 25; 5 26; 27; 28: 113: add 114; ; ; 21 Popular languages such as Java or C# are C + + They now adopt concepts of C++ formerly deprecated New paradigms are discussed, but have to stand the test of time Next generation C++0x is not yet released Many application areas (in particular HPC and Scientific Computing) have not yet fully adopted and understood OOP and C++ This course teaches C++ from scratch. However, it does not follow the historic path neither does it start directly with sophisticated OOP concepts. It rather follows the academic path, i.e. introduces one fundamental concept at a time. As OOP (as a concept) still is considered to be sophisticated in our disciplines, it will be the last thing we talk about. Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 35 of 41

36 1.6. Development Workflow Three Tools Coin Our Work Editor (vi, Emacs, Notepad, whatever) to write simple text files Compiler (g++) invoked on the command line Linker (g++) invoked on the command line Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 36 of 41

37 If Programming Were Cooking... Editor (vi, Emacs, Notepad, whatever)... we would write down with the editor the recipe of one single dish such as the dessert or the main course. The recipe then is the algorithm and it is written down as source code which is typically a simple text file with the extensions.c,.cpp, and so forth. Compiler (g++) Linker (g++) Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 37 of 41

38 If Programming Were Cooking... Editor (vi, Emacs, Notepad, whatever) Compiler (g++)... would take the recipe (source code) and cook it. The results are called object code or object files. They typically have the extension.o. It is invoked by g++ -c filename.c. Linker (g++) Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 38 of 41

39 If Programming Were Cooking... Editor (vi, Emacs, Notepad, whatever) Compiler (g++) Linker (g++)... would take the individual dishes and combine them into a complete meal with several courses. It is invoked by g++ filename1.o filename2.o -o outputfile and produces an executable.... there would be a menu card given by several header text files as well. They typically have the extension.h or.hpp. Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 39 of 41

40 Standard Workflow Write down your source codes (files file1.cpp, file2.cpp,...) into text files with an editor of your choice Write down your descriptions (files file1.h, file2.h,...) (we will do this later as it is a matter of style) into text files with an editor of your choice Open your command line and type g++ -c file1.cpp g++ -c file2.cpp g++ file1.o file2.o myappl./myappl produces file1.o produces file2.o produces executable myappl execute myappl Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 40 of 41

41 Exercise vi first-appl.cpp # i n c l u d e <iostream> i n t main ( ) { std : : cout << Hello yourname ; r e t u r n 0; } g++ -c first-appl.cpp ls g++ first-appl.o -o myappl ls./myappl Einführung in die Programmierung Introduction to C/C++, Tobias Weinzierl page 41 of 41