1 / 72

CS3101-2 Programming Languages – C++ Lecture 1

CS3101-2 Programming Languages – C++ Lecture 1. Matthew P. Johnson Columbia University Fall 2003. Welcome. CS3101-2 Programming Langs: C++ 1 credit, 1/3 semester  same bang/buck as usual (3000-level) 6 weeks, in-class final exam 2-hour sessions First class: overview of Unix, C++

analu
Download Presentation

CS3101-2 Programming Languages – C++ Lecture 1

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. CS3101-2Programming Languages – C++Lecture 1 Matthew P. Johnson Columbia University Fall 2003 CS3101-2, Lecture 1

  2. Welcome • CS3101-2 Programming Langs: C++ • 1 credit, 1/3 semester  same bang/buck as usual (3000-level) • 6 weeks, in-class final exam • 2-hour sessions • First class: overview of Unix, C++ • Magical mystery tour • Others: one or two topics, in depth CS3101-2, Lecture 1

  3. Course Requirements • Assumes previous programming experience • Probably Java or C for most • But neither is required • Will, though compare and contrast between C/C++/Java • O(5) homeworks – 70% • Programming & written • Final exam – 25% • Participation/quizzes/attendance – 5% • Class attendance is required • You’re responsible for all material from lecture • Class time is finite • Responsible for all assigned reading • NB: some material may be covered in lecture xor reading • Lectures may have non-PPT portions • PPTs will be online to complement lecture CS3101-2, Lecture 1

  4. Contact Info • Class page: http://www.columbia.edu/~mpj9/3101-2 • PPTs • In-class examples • Link to CourseWorks, other lecture notes, etc. • Me: mpj9@columbia.edu • OHs: Saturdays, 1-3, in 251 Mudd lab • Check classpage for updates • TA: Jacob Porway • jmp204@columbia.edu • OHs: see web • Check http://ta.cs.columbia.edu for updates • Feedback is good! • Prepend “CS3101-C++” to subject lines! CS3101-2, Lecture 1

  5. Textbook • For the C course, I like: • The C Programming Language (K&R) • Classic text • By creators of C • Short, pretty cheap, and rigorous CS3101-2, Lecture 1

  6. Textbook • This class is C++ • Exists the book: • The C++ Programming Language • By creator of C++ • Rigorous, but difficult, expensive, and long (+1000 pages) CS3101-2, Lecture 1

  7. Textbook • So we’ll use: • Practical C++ Programming • O’Reilly • Available Labyrinth, Papyrus, Amazon and B&N (links on class page) • Not too difficult, not too long (~500 pages) • Lectures will sometimes follow text, sometimes not CS3101-2, Lecture 1

  8. IMPORTANT • I’ll repeat your questions before answering them, for CVN • If I forget, remind me! • Before I’ve answered • Get participation XC CS3101-2, Lecture 1

  9. Rest of this class • Description & History of C/C++ • Intro to Unix • 0th Homework • C++ Tutorial CS3101-2, Lecture 1

  10. (Pre)History of C++ • BCPL (Basic Combined Programming Language), Martin Richards, 1960s • B (typeless), replaces BCPL, Ken Thompson, 1970 • C (fairly strongly typed), successor to B, Dennis Ritchie, Bell Labs, early 1973 • C-With-Classes, Bjarne Stroustrup, 1979 • C++, Bjarne Stroustrup, Bell Labs, 1983 • ANSI C standardization (K&R, second edition), 1988 – … • Java, James Gosling, Sun, 1995 • C#, Microsoft, about 15 minutes ago • C++, Java, C# conserve (much) C syntax CS3101-2, Lecture 1

  11. Description of C • General-purpose language • “Procedural”: functions/procedures (not functional!) • “Imperative”: list of imperatives (commands) • Mid-level • Tricky syntax, but quite small; short learning curve • C programs ~ Hemingway’s “tight, athletic prose” (Scribner blurb) • CU (and others) jumped from C to Java, skipping C++ • Cross-platform language, single-platform compilers (unlike Java) • Char-based CS3101-2, Lecture 1

  12. Why C? • Prior to C, two broad types of languages: • Applications languages • High-level • COBOL, etc. • Portable but inefficient • Systems languages • Low-level • Assembly • Efficient but not portable • Goal of C: fast and portable • How: abstract above hardware arch, but not far! CS3101-2, Lecture 1

  13. Why not C? • But: C is procedural (imperative) • Limited encapsulation • Programs = algorithms, data structures • Relationship between (/tying together of) algs and data they take is manual • Intelligence tends to be widely distributed/decentralized • 10th Amendment/States rights •  Large programs hard to maintain/understand • Dynamic memory management is entirely manual • Need memory at run-time  must request right number of bytes, interpret correctly • When finished, must remember to free that memory • Fast (in part) because there’s so little error-checking • ar[-2] or ar[100000] doesn’t throw an exception (doesn’t support exceptions!) • just gives you read/write access where that elm would be • C simpliciter is multi-platform-compilable but, e.g., graphics/GUI libraries tend to be platform-specific • No types for boolean (just ints), string (just char arrays), etc. • Not multi-threaded • Everything in same namespace ( naming collisions) • All arg-passing is pass-by-value; must simulate pass-by-reference with pointers CS3101-2, Lecture 1

  14. Why Java? • Java is object-oriented • Has garbage-collection • Prevents making of many mistakes legal in C • Stricter typing  so prevents many mistakes legal in C/C++ • J has much more error-checking • Primitive array replaced with (implicit) array object • J has exceptions • a[-2] throws exception • Is multi-platform-runnable (compile once; run anywhere) • Has types for boolean, string*, etc. • Is multithreaded • Has packages for organizing classes to prevent naming collisions • All objects automatically pass-by-reference; all primitives pass-by-value •  Java is great • Very sexy for a long time, throughout boom • Lots of universities skipped from C to Java • Q: any reason to learn C++, then? CS3101-2, Lecture 1

  15. Why C++? • A: Yes! • Java is very elegant, but it doesn’t compile to machine code •  It’s very slow! • O(20) times slower than C/C++ • Compiled Java programs aren’t executables, they’re .class’s • They’re run not by OS but by JVM (java.exe) • Big idea: write JVM for web browser on every platform people use (i.e., all 3 of them) •  any browser can run your applet • Notice: winword.exe, netscape.exe, etc., aren’t class files • Almost all “real” PC/Mac software, Windows itself, many JVMs were written in… • C++ • C++ has a steeper learning curve • so Java is the dept’s default lang, learned over a semester or two • Instead, we’ll learn C++ in 6 weeks CS3101-2, Lecture 1

  16. What is C++/OOP? • C++ is the successor language to C • At a high level: C++ ~= C + OOP • Big idea of OOP: organize the world into intelligent objects • The objects aren’t good at trivia questions • They’re able to solve the problems relevant to themselves • Plato: “carve nature at its joints” • Concepts/sorts of things in world  classes • Particular examples of those things  objects • Each object has • its own data • Access to functions applicable that data • Big argument in favor of OOP over imperative languages: • An imper program is just an abstracted list of assembler commands, which is just an abstracted list of machine code commands  written with the machine in mind • An OOP program is an abstraction of the concepts and problems you’re interested in  written with your interests in mind CS3101-2, Lecture 1

  17. OOP Concepts • Object legislates how its data may be accessed (encapsulation) • Some data may be accessible to others, some not • Data can only be modified in specified ways  easier to ensure correctness • One class may be a special case of another (inheritance) • Rectangle is like a square, plus a second (possibly) distinct value • Colored-Rectangle is like a rectangle, plus the concept of color • Different classes in a hierarchy behave correctly (polymorphism) • shape.getArea()  len*wid, if shape is a rectangle • shape.getArea()  PI*r2, if shape is a circle • Most important of three: encapsulation CS3101-2, Lecture 1

  18. Why C++? • C++ is OOP and procedural • No garbage collection, but dynamic memory simpler than in C • Both safer and not safer • Still has prim. array, but also has safer/slower array-like objects • Somewhat stricter typing than in C • New casting somewhat safer, but old casting still unsafe • Still only cross-platform-compilable, for most char-based programs • Standard Template Library includes many important data structs & algs • Like Java, has a boolean type and a string class • Still not multi-threaded • Has namespaces to prevent naming collisions • Can pass objects by reference • Also, can pass both objects and primitives by value, by reference, or by pointer • Supports function overloading (like Java) • Supports operator overloading (unlike Java) • Supports default function parameter values • Has multiple inheritance (only single inheritance in Java) • Has templates (“generics” in Java 1.5) • Many other changes we’ll see as we go along CS3101-2, Lecture 1

  19. What is C++? • C++ is (almost exactly) a superset of C • C concepts are also C++ concepts • Although many have C++ replacements/analogs • (Almost) Every valid C program is a valid C++ program • The set of C++ programs contains the set of C programs • Exceptions: use of new C++ keywords as var names, e.g. • One strategy for learning C++: • Learn C • Learn (C++ - C) • For most part, we won’t follow this strategy in this class • If you took 3101-1, then you’re following this strategy this semester • In general, we introduce concepts as they appear • Comparing/contrasting with C, Java analogs as applicable • Will be some overlap at beginning – basic syntax, shared concepts • Overlap should diminish rapidly • NB: Many tasks can be done C-style or C++-style • In general, lose points for C-style if C++-style has been covered CS3101-2, Lecture 1

  20. Unix • You don’t have to do your hw on newcunix • Can download for free Borland C++ from class page • But hw must be submitted with newcunix submit script; • hw must compile on Unix (with g++) to be graded • Can Sftp and recompile before submitting • Non-compiling hw will not be graded! • Editors on newcunix: Emacs, Pico, etc. CS3101-2, Lecture 1

  21. Programming with Emacs/g++ CS3101-2, Lecture 1

  22. g++ Tips • Compilers on newcunix: • CC (default compiler; not “cc”) • g++ 3.3 (GNU’s C++ compiler) • Ensure you use the right version • Add these lines to your .profile (in your ~) • export PATH=/opt/gcc-3.3/bin:$PATH • export LD_LIBRARY_PATH=/opt/gcc-3.3/lib:$PATH • Instructions will be online • Compile with warnings on –Wall • Fix the first error first • One typo can cause huge numbers of errors • Send lots of messages to screen if confused CS3101-2, Lecture 1

  23. Unix Commands CS3101-2, Lecture 1

  24. Submitting from newcunix • Instructions: • Put hw in its own directory • Re-compile with g++ • $ /opt/ACISsubmit/bin/submit cs3101-2 • Wait for email confirmation • Important: • Omits binary files, *~ (backups) • Submits all text files in and below current directory • Don’t submit from your ~ directory! • Hw submitted by email will not be graded! Important: • Q: Can I just email in first hw? • A: No! Learning how to compile & submit is the purpose of hw0 CS3101-2, Lecture 1

  25. Where to code • On newcunix: Emacs, Pico, etc. • On Win: Fancy IDEs like VC++, C++Builder, etc. • I recommend Textpad (textpad.com) • FTP: use utility, or put sftp://newcunix.cc.columbia.edu in IE address bar, log in, drag&drop CS3101-2, Lecture 1

  26. Homework 0 • Write, compile, and run a Hello, World program • Prints “Hello world, from <my name>.” • Hand in: • Source file (e.g., hello.cpp) • Trace file ($ hello > trace.txt) CS3101-2, Lecture 1

  27. Collaboration Policy • All subsequent work • Must be done independently • Collaboration = cheating • See scary CU cheating policies • “Severest of conseqences” •  deans, honor committees, not fun • This homework only • Collaboration is fine • Hw0 is “merely instrumental”: learn how to compile & submit CS3101-2, Lecture 1

  28. C++ Tutorial • Quick & dirty intro to language • Learn to write by writing, learn to program by programming • First program: Hello, World • #include <iostream> main() { std::cout << “Hello, world.” << std::endl; } CS3101-2, Lecture 1

  29. C++ Tutorial – Hello, World • In Java, a program is >= 1 class • In C, a program is >= 1 function • In C++, a program is >= 1 function + >=0 classes • In all three, main() is the entry point • Contains the instructions performed when program is run • The body of a ftn is demarcated by braces (“curly brackets”): { } • Inside, instructions to be performed when ftn is called • main() is called on program start-up CS3101-2, Lecture 1

  30. C++ Tutorial - #include • Before main() function, we have • #include <iostream> • Tells compiler to include the iostream (no .h!) library • Operationally similar to Java’s import • # indicates command to C Preprocessor (CPP) • Preprocesses the source just before compilation • #include line replaced with contents of file • What’s included is the header/declaration for a library • The library’s public interface • Allows access to functions and objects in the library • System libraries in < >, one’s own in “ ” CS3101-2, Lecture 1

  31. C++ Tutorial – cout • Our program contains one statement: a call to std::cout • std “standard” library namespace • cout “console output” stream • Similar to Java’s System.out.print() and C’s printf() • printf uses complicated pattern-matching for outputting computed expressionss • print() and cout use OO • each object/var knows how to be printed • Intuitive (for now) understanding of << op: • Param is being passed (left) to cout CS3101-2, Lecture 1

  32. C++ Tutorial - Parameters • We passed “Hello, World.” and endl to std::cout as a parameter • Tells function what to do • In this case, what to print • endl is a stream manipulator • Not simply data to be printed • Tells cout to print ‘\n’ and flush the stream • ’\n’ is the new line escape character CS3101-2, Lecture 1

  33. C++ Tutorial – Esc chars • Stores internally as a char (1-byte integer) • A char-based concept • Not corresponding to any actual/typable character CS3101-2, Lecture 1

  34. C++ Tutorial - Temps • More complicated program – print table of Fahr. – Cels. temperatures: • Math? • C = 5/9 * (F-32) CS3101-2, Lecture 1

  35. C++ Tutorial - Temps #include <iostream> // prints F-C table main() { int lwr = 0, upr = 300, step = 20; int fahr = lwr; while (fahr <= upr) { int cels = 5*(fahr-32)/9; std::cout << fahr << ‘ ‘ << cels << std::endl; fahr = fahr + step; } } CS3101-2, Lecture 1

  36. C++ Tutorial – Temps – comments • Things to notice: • /* */ enclose comments – no effect on program • // for single line comments • /* */ //, mutually nest • Can also comment code using CPP: • #if 0 this stuff won’t be seen by the compiler la LA la la laaaaa #endif • Three kinds of commenting syntax (CPP/C/C++) • But avoid CPP unless necessary (like #include) CS3101-2, Lecture 1

  37. C++ Tutorial – Temps – vars • Var declarations • Announce that fahr, etc, will be names of persistent pieces of data, of type int • Var types determine what sort of value a var can take on • Local vars can be declared anywhere in a block (like in J) • Not just at beginning of block (like in C) • Live until end of block defined in • Var names: letters, digits, _ (can’t begin with digits) • Case-sensitive (like all else) • Other var types: • long (large integers) • floats (rational numbers) • doubles (larger, higher precision floats) • chars (small integers, representing typographical symbols) • bools (not booles, in spite of his name) CS3101-2, Lecture 1

  38. C++ Tutorial – primitive types • Many data type sizes are … • undefined, i.e., compiler/machine-dependent (as in C) • Restrictions (in bytes): • |char| == 1 < |short| <= |int| <= |long| • Often: • |short| == = 16  -32768…32767 • |int| == |long| = 32  -1038…1038 • Integer literals (e.g, 10) eval as ints • Char literals (e.g., ‘A’) eval as chars • Unlike in C; overloading • NB: Don’t include leading 0s unless you mean it: 011 • This is octal: 011 == 1 + 8 == 9 CS3101-2, Lecture 1

  39. C++ Tutorial – Temps - assigns • Like in C/Java: value of RHS stored in LHS • lvalue == can appear on LHS of assignment (e.g, vars) • rvalue == merely passive value • Assignments are expressions • with side effects (i.e., rvalue assigned to lvalue) • x = 10 x == 10 • that eval to some val (the new val of the lvalue) • (i = static_cast<int>(3.5)) val of i == 3 • Statements terminated by ; • More generally: • Statement == expr + ; CS3101-2, Lecture 1

  40. C++ Tutorial - Temps • Table lines all of same form: two numbers, with a certain relationship  repetition  print lines the same way • Here using while-loop • Repeated evals test condition; if passes test, execs while body • While body is a statement or block of statements CS3101-2, Lecture 1

  41. C++ Tutorial - Temps • Celsius computation line: • cels = 5*(fahr-32)/9; • Why not this: • cels = 5/9*(fahr-32);? • val1 and val2 are of the same type  the value of val1 op val2 will also be of that type  5 and 9 are ints  5/9 is an int  5/9 as an int is just 0  all Celsius temps become 0 CS3101-2, Lecture 1

  42. C++ Tutorial - Temps • cout line: • std::cout << fahr << ‘ ‘ << cels << std::endl; • Similar to Java equiv: • System.out.println(fahr + ‘ ‘ + cels); • Much different from C equiv: • printf(“%d %d\n”, fahr, cels); • NB: in both C and C++, must specify end-of-line manually: endl or ‘\n’ CS3101-2, Lecture 1

  43. C++ Tutorial – Temps’ •  use floating-pts for greater precision • double f = 0, c = 0; while (f <= upr) { c = (5.0/9.0) * (f – 32.0); std::cout << fahr << ‘ ’ << cels << std::endl; } • No need to change output • cout knows how to handle doubles, too CS3101-2, Lecture 1

  44. C++ Tutorial – Temps’ • More succinct with a for loop: • main() { for (int f = 0; f <= 300; f += 20) std::cout << fahr << ‘ ’ << (5.0/9)*(f–32) << std::endl; } • Notice: • Fewer vars • sent expr (not var) to cout • << has low precedence • Doesn’t use float in <= check • Used +=: a += b  a = a + b • Can declare counter var in for-loop init CS3101-2, Lecture 1

  45. C++ Tutorial – Temps’ • For loop pattern: • for (init; test; inc) {}  • init; while (test) { /* body code */ inc; } • For loop var lives past for loop body, just as in while-loop analog • Infinite loops: • while(true) … • for (;;) … CS3101-2, Lecture 1

  46. C++ Tutorial – Temps’’ • In general: hard-coded, frequently appearing literals (“magic numbers”) are bad • Soln 1: symbolic constants • Defined with preprocessor – no ; • Pattern: #define name replace-text • Replaces all occurrences except: • In “ ” • In part of other name • Soln 2: declare numbers as consts CS3101-2, Lecture 1

  47. C++ Tutorial – Temps’’ const int LOWER = 0, UPPER = 300, STEP = 20; // … main() { for (int f = LOWER; f <= UPPER; f += STEP) std::cout << f << ‘ ’ << (5.0/9)*(f–32) << std::endl; } CS3101-2, Lecture 1

  48. C++ Tutorial – Temps’’ output $ g++ temp1.cpp $ a.out 0 -17.7778 20 -6.66667 40 4.44444 60 15.5556 80 26.6667 100 37.7778 120 48.8889 140 60 160 71.1111 180 82.2222 200 93.3333 220 104.444 240 115.556 260 126.667 280 137.778 300 148.889 • Coding is now okay • But output is ugly • Uneven columns – based on number-width • Cels show too many dec. places • Improvement 1: replace ‘ ‘ with ‘\t’ CS3101-2, Lecture 1

  49. C++ Tutorial – Temps(2) output $ g++ temp2.cpp $ a.out 0 -17.7778 20 -6.66667 40 4.44444 60 15.5556 80 26.6667 100 37.7778 120 48.8889 140 60 160 71.1111 180 82.2222 200 93.3333 220 104.444 240 115.556 260 126.667 280 137.778 300 148.889 $ • Output is better • Aligned left • But still ugly • Numbers should right-align • Cels show too many dec. places • Improvements 2. create columns with column-widths, not tabs; 3. right-align columns CS3101-2, Lecture 1

  50. C++ Tutorial – Temps(3) #include <iostream> #include <iomanip> using namespace std; const int LOWER = 0, UPPER = 300, STEP = 20; main() { for (int f = LOWER; f <= UPPER; f += STEP) { cout.width(3); cout << f; cout << setw(7) << (5.0/9)*(f-32) << endl; } } CS3101-2, Lecture 1

More Related