Computer Programming and Utilization CS101 Spring 2012

1. Computer Programmingand UtilizationCS101 Spring 2012 Soumen Chakrabarti with CS101 TAs and Staff

2. First steps • http://www.cse.iitb.ac.in/~cs101/ • Fill out survey when survey link appears • Find out your lab batch Eighty percent of success is showing up. Woody Allen CS101 2012.1

3. Places and times • Lectures (two sections) • Slot 10: Tu, F 2—3:30 • Slot 6: W, F 11—12:30 • Labs (OSL) • Four evenings a week, plus one makeup • Tutorial • Depends on interest S10 (160) M T W Th F S6 (160) (80) Make-up lab CS101 2012.1

4. “The management” cs101.iitb@gmail.com Web site STAs Instructor Assignment STAs STA STA STA STA STA cs101stas@cse.iitb.ac.in JTAs JTAs JTAs JTAs JTAs cs101jtas@cse.iitb.ac.in Thu lab. batch Tue lab. batch Wed lab. batch Fri lab.batch Make-up lab. Do not use personal email CS101 2012.1

5. Assessment • Midterm exam and quizzes • Two to three exams • Total 25—35% • Final exam • 30—40% • Some lab. sessions will be graded • 15—20% • Project and viva • 5—10% CS101 2012.1

6. PC building blocks: motherboard CPU withcooling fan Fastelectronicmemory Magneticdisk dataconnectors CS101 2012.1

7. Storage and peripheral devices Keyboard Display Rotatingmagneticplatters Record/playhead on arm Data cable betweendisk and motherboard CS101 2012.1

8. Simplified abstract view CPU Random accessmemory (RAM) RAM location 0 Arithmeticand logic unit Address RAM location 1 RAM location 2 … Register 0 Register 1 Data Reserved fordisplay Register 2 … Reserved for keyboard Program that tells the CPU what to do andhow to do it CS101 2012.1

9. Rules of the game • A register or a RAM location can store exactly one value at any time • Writing into a register or RAM location (or reading into it from the keyboard) destroys the earlier value • Outputting a register or RAM location to the display is done by copying to the area reserved for the display; this does not destroy the source value • Accessing any RAM location is equally fast CS101 2012.1

10. E.g.: Centigrade and Fahrenheit • C/5 = (F-32)/9 • Painful to say “register 5” and “RAM location 43” so we will use shorter names • Load input F from keyboard into R0 • Load 32 into R1 • Store R0R1 in R2 • Load 9 in R3 • Divide R2 by R3 and store in R4 • Load 5 in R5 • Multiply R5 by R4 and store in R6 • Output R6 to the display “Assemblylanguageprogramming” Painful! CS101 2012.1

11. High level programming language • Programmer need not keep mental map of which register and RAM location contain values of what symbolic variables • Compiler or interpreter automatically translates from above format to register and RAM location manipulations we saw • Input F from keyboard • Set C to 5*(F-32)/9 • Output C to display CS101 2012.1

12. Saying it in C++ Variable type main() { float fahrenheit; cin >> fahrenheit; float centigrade = 5*(fahrenheit-32)/9; cout << centigrade; } Procedure name Variable declaration Arithmetic expression • Some details omitted • Save above source code to text file • Compile source code to executable file • Call executable from a shell command line CS101 2012.1

13. The hardware-software stack Your C++ executable program Shell command line (bash) Operating System (Linux) Ha Hardware Your program accesses resources like CPU, keyboard,display, through the lower layers of system software CS101 2012.1

14. C++: More detail main() { float fahrenheit; cin >> fahrenheit; float centigrade = 5*(fahrenheit-32)/9; cout << centigrade; } Procedure name Variable declaration Data type Arithmetic expression • What is a procedure? • What are data types? • Where did cin and cout come from? • Rules of writing arithmetic expressions CS101 2012.1

15. Procedure or function • Encapsulates a piece of computation and gives it a name • E.g. main is the default procedure that is run when your program is executed from the shell • May accept input values stored in named variables • E.g. int max(int a, int b) • And return output value • E.g. max(-3, 2) should return 2 CS101 2012.1

16. Data types • Computer memory is a 2d array of bits • Eight columns (one byte or “B”) • Rows depends on how much memory you have; “1 GB” means 1,073,741,824 rows • Hard disk is similar, only larger and slower • What programmers want • Integers, real numbers, complex numbers • Characters, strings of characters • Arrays, variable length lists, mappings • Windows, buttons, menus • Will study how many of these are represented in memory CS101 2012.1

17. Choosing names • C++ allows any sequence of characters A—Z, a—z, 0—9, and underscore • Not starting with a digit • Up to some maximum number of characters • old_style_variable_name • newStyleVariableName (“camel case”) • turbineRPM or turbineRpm? CS101 2012.1

18. cin and cout • “Console in” (keyboard) and “console out” (display) • These variables are not defined magically • To use them, must prefix our C++ code with instruction to include a header file like this:#include <iostream> • The operating system and compiler work together to let your code access the keyboard and display through cin and cout • Not quite… CS101 2012.1

19. Namespaces • We must write std::cin and std::cout • Two different Ravi Vermas in hostels 2 and 5 • To avoid confusion, write asH2::RaviVerma and H5::RaviVerma • Lets libraries written by different people avoid variable and function name clashes • std is the “standard” namespace within which C++ predefined variables and functions are provided CS101 2012.1

20. The std namespace and using • Tedious to type std:: in front of everything • If you are not using too many namespaces simultaneously, you can choose a default by sayingusing namespace std;before using things defined inside std. CS101 2012.1

21. First complete source code #include <iostream> using namespace std; main() { float fahrenheit; cin >> fahrenheit; float centigrade = 5*(fahrenheit-32)/9; cout << centigrade; } • At your shell, typeg++ cf.cc • Now run resulting file as./a.out Save to file “cf.cc” g++ compiler Executable a.out CS101 2012.1

22. Files • cf.cc and a.out are files • A file is a sequence of bytes • These bytes can be interpreted differently depending on the applications that read or write the files • cf.cc is a text file to be written by a programmer and read by the C++ compiler • Any name ending in .cc or .cpp is ok • a.out is an executable file to be run from the shell command line • You can rename this file as you wish CS101 2012.1

23. Disk organization: Directories • A directory is a container that can contain files and other directories • Files cannot contain directories • Tree hierarchy of directories • Root is “slash” / • Full path written as/usr/bin/g++ / home usr bin cs101 you g++ bash CS101 2012.1

24. Compilation and execution summary string math.h Source code cf.cc iostream g++ compiler main() function in a.out C/C++ execution environment string math iostream Bashshell char, short, int, float, double, if, switch, while, … Headerfiles Operating system (Windows, Linux, Mac OS, …) Precompiled libraries CPU RAM Disk Keyboard Display CS101 2012.1

25. Visual programming: Turtle graphics • “Turtle” holding pen • Initially touching paper • Turn through angle • Move some distance • Pen down, pen up forward(100); left(90); forward(100); left(90); forward(100); left(90); forward(100); Repititive and boring CS101 2012.1

26. Blocks and loops • Want to draw arbitrary regular polygons • Input: numSides (number of sides) • Repeat numSides times: • Move through a fixed length, say 100 units • Turn anticlockwise by 360/numSides degrees int numSides; cin >> numSides; repeat(numSides) { forward(100); left(360/numSides);} Red text shows a block of instructions to be executed in sequence (What will happen if 360/numSides isfractional?) CS101 2012.1

27. 1st lab session • Familiarize with Linux desktop • Open a terminal window, the bash shell • Your home and other directories; files • Running shell commands • Using a text editor • Typing a small C++ program • Compiling it using g++ • Running the resulting executable file CS101 2012.1