Understanding Operating Systems and Programming in C: Course Overview

1. Administration • Lecturer • Abed Asi(abedas@cs.bgu.ac.il) • Lab assistants • David Tolpin – tolpin@cs.bgu.ac.il – Monday 16:00 – 19:00 • Abed Asi – Wednesday 16:00 – 19:00 • Office hours • Sunday 14:00 – 16:00 (-102/37) • Website • www.cs.bgu.ac.il/~espl141 Abed Asi - ESPL

2. Administration • Lectures and Labs • One-hour lecture every 2 weeks (with two exceptions) • 12 (or 11) Lab sessions • Quizzes • 2 Quizzes • NOfinal exam • Grading policy • 40% for quizzes (20% per quiz) • 60% Labs (5% per lab) Abed Asi – ESPL

3. Lab Instructions • http://www.cs.bgu.ac.il/~espl141/Main Abed Asi – ESPL

4. Lectures schedule Abed Asi - ESPL

5. Today • Unix environment • Data types in C • C – simple programs • C Arrays – A Glance • Makefiles • Java vs. C Abed Asi - ESPL

6. What is an Operating System? • A program that starts up when you turn on your computer and runs underneath all other programs • It is a manager. It manages all the available resources on a computer, from the CPU, to memory, to hard disk accesses • Tasks the operating system must perform • Control Hardware - attempts to get everything working together • Run Applications– running applications software such as: word processors, web browsers, games, etc... • Memory Management - controls the mapping between logical memory and the hard disk, managing file system and more .. Abed Asi - ESPL

7. Unix OS: Brief History • The UNIX operating system was born in the late 1960s. • It originally began as a one man project led by Ken Thompson of Bell Labs • Grown to become one of the most widely used operating system • It has gone through many different generations and even mutations • Some differ substantially from the original version, like Berkeley Software Distribution (BSD) or Linux. • Others, still contain major portions that are based on the original source code. Abed Asi - ESPL

8. Unix OS: Overview • The Kernel - handles memory management, input and output requests, and program scheduling. Technically speaking, the kernel is the OS. • The Shell - basic UNIX shells provides a “command line” interface which allows the user to type in commands. • The Built-in System Utilities - are programs that allow a user to perform tasks which involve complex actions such as listing the content of directories, move & copy files, remove files, etc... • Application Software & Utilities – additional programs that are bundled with the OS distribution, or available separately. There are not part of UNIX Abed Asi - ESPL

9. Programming in Unix Environment • To develop your own program you need: • Compiler: translates your programming language to assembly • Text editor: to type down source code • Project management tool: dependencies, linking, executable .. • In Unix: • You will use the gcc compiler • Any text editor that you prefer (Kate, Emacs, KWrite, …) • make as the project management tool • Use Unix Manual for function/program description and more Abed Asi - ESPL

10. Data types • Char • char is the basic type in C • sizeof(char) = 1 byte by definition • Examples: • char c = ‘A’; • char c = 65; Abed Asi - ESPL

11. Data types • int , short, long • sizes: machine dependent! • sizeof(short) <= sizeof(int) <= sizeof(long) • For example: (linux on pentium) • short: 16 bit, int: 32 bit, long: 32 bit • All can be signed/unsigned • Default: signed • unsigned int: [0, 231 -1] • signed int: [-231, 231 -1] Abed Asi - ESPL

12. Boolean types • Boolean types • Doesn’t exist in C ! • Use char/int instead • zero = false • non-zero = true while (1) { … } (infinite loop) if (-1974) { .. } (true statement) Abed Asi - ESPL

13. Programming in C – First program #include <stdio.h> int main() { inti; // declares i as an integer int j = 0; // declaresjas an integer, and initializes it to0 // for( initial ; test condition ; update step ) for( i = 0; i < 10; i++ ) { j += i; // shorthand for j = j + i printf("%d %d %d\n", i, j, (i*(i+1))/2); } return 0; } Abed Asi - ESPL

14. First Program – Compiling and running > gcc–Wall loop.c –o loop > loop 0 0 0 1 1 1 2 3 3 3 6 6 4 10 10 5 15 15 6 21 21 7 28 28 8 36 36 9 45 45 Abed Asi - ESPL

15. Programming in C – Second program #include <stdio.h> /* count number of words in sentence */ int main(intargc, char **argv) { inti;   printf("There are %d words in phrase '", argc-1);   for(i=1; i!=argc; ++i) { printf("%s", argv[i]);   if(i!=argc-1) printf(" "); } printf("'.\n"); return 0; } Abed Asi - ESPL

16. argv & argc: example $> prog –u danny –p 1234 argc = 5 argv[0] = “prog” argv[1] = “-u” ... argv[4] = “1234” Always: argv[5] = 0 Abed Asi - ESPL

17. Arrays • C does not provide array operationsinta[4]; int b[4]; ... a = b; // illegal if( a == b ) // illegal • intarr[5][7]; • 5 rows, 7 columns • continuous memory (divided to 5 blocks) • access: arr[row][col] = 0; Abed Asi - ESPL

18. Arrays • C does not provide any run time checks • This will compile and run (no errors) • But can lead to unpredictable results • It is the programmer’s responsibility to check whether the index is out of bounds… int a[4]; a[-1] = 0; a[4] = 0; Abed Asi - ESPL

19. Array initialization intarr[3] = {3, 4, 5}; // Good intarr[] = {3, 4, 5}; // Good - The same intarr[4] = {3, 4, 5}; // Bad style - The last is 0 intarr[2] = {3, 4, 5}; // Bad intarr[2][3] = {{2,5,7},{4,6,7}}; // Good intarr[2][3] = {2,5,7,4,6,7}; // Good - The same intarr[3][2] = {{2,5,7},{4,6,7}}; // Bad intarr[3]; arr = {2,5,7}; // Bad - array assignment only in initialization Abed Asi - ESPL

20. Compilation • Takes input C-code and produces machine code (object file) • gcc –c Main.c –o Main.o • Main.c Main.o • The object file does not contain all external references • It leaves names, such as “printf”, “area”, etc. as undefined references Abed Asi - ESPL

21. Square.c Square.o Main.c Main.o Preprocessor Compiler Linker Linking • Combines several object files into an executable file • No unresolved references Main libc.a Abed Asi - ESPL

22. Square.c Square.o Main.c Main.o Preprocessor Compiler Linker Linking $ gcc –c Square.c –o Square.o $ gcc –c Main.c –o Main.o $ gccSquare.oMain.o –o Main Main libc.a Abed Asi - ESPL

23. Makefile • What is it good for ? • Automatic tool for projects management • Less boring work for the programmer • Less errors mywc: mywc.c gcc -Wall mywc.c -o mywc Abed Asi - ESPL

24. Makefile – compilation and linkage Makefile prog1: read.omain.olist.ogccmain.oread.olist.o –o prog1 main.o: main.cread.hlist.hgcc -c main.c read.o: read.cread.hgcc -c read.c list.o: list.clist.hgcc -c list.c $ make prog1 prog1 main.o read.o list.o read.c read.h main.c list.c list.h Abed Asi - ESPL

25. Makefile – compilation and linkage • If only one file is modified, will we have to recompile all over again? prog1 • No, the Makefile uses the dependencies tree main.o read.o list.o read.c read.h main.c list.h list.c Abed Asi - ESPL

26. Makefile – dependencies tree • If read.h is modified, what should be done? prog1 • We have to recreate a subset of the files main.o read.o list.o read.c read.h main.c list.h list.c Abed Asi - ESPL

27. Makefile – summary • Aim: build only out-of-date files (use timestamps) • Makefile contains: • List of dependencies (no cycles) • “Recovery” scenario when any file is modified • If any of the files [main.c, list.h, read.h] wad modified after main.o, the command “gcc –c main.c” will be invoked • By default, makeonly executes the first target in the makefile main.o: main.clist.hread.h <tab> gcc-c main.c Abed Asi - ESPL

28. Makefile Read about the explicit and implicit rules for Makefiles Abed Asi - ESPL

29. Java vs. C Abed Asi - ESPL