CS 211

1. CS 211 Recitation 1 TA: Ishani Chakraborty

2. Admin stuff • Email: ishanic@cs.rutgers.edu • Office hours: 5:00-6:00 pm, Tuesdays at Core Bldg, room 246. • Switching recitations is allowed, missing them is not ! • Please follow the instructions for turning in projects. • Check the course webpage every day. - http://www.panic-lab.rutgers.edu/users/peery/cs211/

3. Programming review • Programming paradigms • Procedural(C)– programming task broken into • Variables • Data structures • PROCEDURES • Object oriented (Java) – task broken into • OBJECTS

4. Sample C program /*The first C program*/ #include <stdio.h> int main(void) { printf(“hello, world!\n"); return 0; }

5. Editing • How do you write the code? Popular editors: vi, emacs… • Compiling • How to convert source code to executable code? We use gcc (GNU Compiler Collection) as the compiler.

6. Compiling code $ gcc hello.c • creates file a.out • Execute by typing $ ./a.out $ gcc –o hello hello.c • Creates file hello • Execute by typing $ ./hello make hello

7. The three steps • $ vi hello.c • Write code, save, exit. • $ gcc –o hello hello.c • $ ./hello

8. vi editor: Quickstart • $ vi hello.c • Press i (for inserting text) • Start writing code • When finished, press escape key (to exit editing mode) • Type $ :wq to save and exit • Type $ :q! to quit without saving changes

9. vi editor: Quickstart • To make any changes eg delete, cut, copy etc. exit the editing mode by pressing the escape key.

10. Emacs editor • $ emacs hello.c • A good tutorial link –http://www.cs.colostate.edu/helpdocs/emacs.html

11. Multiple files • A complex program can and should be broken into multiple source files. • To illustrate we look at a simple program with 4 files • main.c • hello.c • factorial.c • functions.h

12. main.c functions.h void print_hello(void); int factorial(int n); #include <stdio.h> #include "functions.h“ int main(void) { print_hello(); printf("\n"); printf("The factorial of 5 is %d\n",factorial(5)); return 0; } hello.c factorial.c #include "functions.h" int factorial(int n) { if(n!=1){ return(n * factorial(n-1)); } else return 1; } #include <stdio.h> #include "functions.h“ void print_hello() { printf("Hello World!\n"); }

13. $ gcc main.c • $ gcc –c main.c

14. gcc-ing with –c flag creates an object file that is independent of other files. • gcc-ing without –c flag = compiling and linking files, so interdependent files have to be compiled together. $ gcc main.c hello.c factorial.c –o hello

15. Makefile • Compilation of several programs whose files are dependent on one other ? • When making changes to one(few) file(s), several files remain unchanged so don’t need to compile them. • make recompiles only those files that need to be updated (Looks at the timestamps of source files, if source files newer than object files, recompile.)

16. Makefile • Set of rules target: dependencies [tab] system command myprog.o: myprog.c myprog.h gcc –o myprog myprog.c Target Dependency list [tab] Action(s) to create the target

17. Makefile-1 all: gcc -o hello main.c hello.c factorial.c

18. Makefile-2 all: hello hello: main.o factorial.o hello.o gcc main.o factorial.o hello.o –o hello main.o: main.c gcc -c main.c factorial.o: factorial.c gcc -c factorial.c hello.o: hello.c gcc -c hello.c

19. Makefile-3 # Variable CC will be the compiler to use. CC=gcc # Set the CFLAGS options to be passed to the compiler. CFLAGS=-c –Wall all: hello hello: main.o factorial.o hello.o $(CC) main.o factorial.o hello.o -o hello main.o: main.c $(CC) $(CFLAGS) main.c factorial.o: factorial.c $(CC) $(CFLAGS) factorial.c hello.o: hello.c $(CC) $(CFLAGS) hello.c

24. Admin stuff • Recitation ppts uploaded at: http://www.research.rutgers.edu/~ishanic/cs211/cs21109.htm • Project 1 due: 16th Feb ’09. • https://handin.rutgers.edu • Single tar file • If your files are in folder called project1 use the command tar -cvf project1.tar project1

25. Debugging • Bug: Error/fault in a computer program producing incorrect/unexpected results. • A simple debugger: print statements in code. • Code needs recompilation every time. • Guess the source of the problem. • Impractical in complex programs. • Debuggers are powerful and flexible.

26. Factorial function (fact.c) #include <stdio.h> int factorial(int); void main(void) { int number; printf("Please enter a positive integer: “); scanf("%d",&number); if (number < 0) printf("That is not a positive integer.\n”); else printf(“The factorial of %d is %d“,number,factorial(number)); } int factorial(int number) { int temp; if(number <= 1) return 1; temp = number * factorial(number - 1); return temp; }

29. gdb basics • GNU debugger • gcc –g source • gdb executable • run • list • break • step • backtrace • print

30. list

34. So we have written, compiled, ran and debugged a code. • Now we will focus on what goes into a code, namely data and their structures. • Data structures eg arrays, structures, unions, stacks, queues, trees etc…

35. Arrays • Group of elements accessed by indexing. • Elements have same data type. • Placed in contiguous memory locations.

36. Arrays • char foo[80]; • – An array of 80 characters • – sizeof(foo) • = 80 × sizeof(char) • = 80 × 1 = 80 bytes • int bar[40]; • – An array of 40 integers • – sizeof(bar) • = 40 × sizeof(int) • = 40 × 4 = 160 bytes

37. Nested Arrays • 2D array A • int A[4][3] • Space required to store A ?

38. Element Address int A[4][3] = { {1, 2, 3}, {4, 5, 6}, {7,8, 9}, {10, 11, 12} };

39. Structures • Heterogeneous data structure: • Elements can have different data types. • Contiguous memory locations.

40. structures #include <stdio.h> struct data { char name; struct { int age; int height; } s; }; int main(void) { struct data cs211; cs211.name = ‘H’; cs211.s.age = 21; printf("%c is %d years old\n", cs211.name,cs211.s.age); return 0; }

42. What does this program do ? #include <stdio.h> #define ITERATIONS 20 int main() { int num[3]={0,1}; int count1, count2; printf("%d %d ", num[0], num[1]); for (count1=0; count1 < ITERATIONS-2; count1++) { num[2] = num[0] + num[1]; printf("%d ",num[2]); for (count2 =0; count2 < 2; count2++) num[count2] = num[count2+1]; } printf(“\n”); return 0; }

44. What does this program do ? #include <stdio.h> int main(int argc, char* argv[]) { int i; printf("%d arguments\n", argc); for(i = 0; i < argc; i++) printf(" %d: %s\n", i, argv[i]); return 0; }