1 Lab 2: The Unix environment, Using vi, C programming SITE, uOttawa

2 Practical tools Editor Editor Vi (emac) Vi (emac) Compiler Compiler gcc gcc Makefile Makefile make make Debugging Debugging gdb gdb

3 Using C/Unix/Linux at SITE $ ssh linux

4 Vi Editor A screen-based editor used by Unix users An experience with vi Starting the editor Cutting and Pasting/Deleting text Inserting New Text Moving the Cursor Within the File Moving the Cursor Around the Screen Replacing Text Searching for Text or Characters Saving and Quitting

5 Vi Basic Commands mkdir - create a directory cp - copy a file rm - delete a file vi - open a file pressing the key turns off the Insert mode :q – quit with saving :x – quit without saving :i – insert text before cursor, until hit :a – append text before cursor, until hit $ - move cursor to the end of the current line :w – move cursor to the beginning of next word 0 – move cursor to the start of current line :o – open and put text in a new line after the cursor y1 – copy current character Yn – copy n characters yy – copy current line p - paste characters x – delete single character under cursor dd – delete the current line u – undo the last action :w – save a file / - search the string forward ? - search the string backward

6 Avi Exercise Create and edit test.c file Create and edit test.c file #include #include main(){ printf(“Hello world, …\n”); printf(“Hello world, …\n”);}

7 C programming/Unix #include #include main(){ printf(“hello, wolrd…\n”); printf(“hello, wolrd…\n”);} $ mkdir csi3130 $cd csi3130 $ vi test.c $cc test.c $a.out

8 Compiler GNU Compiler Collection GNU Compiler Collection A compiler system produced by the GNU Project supporting various programming languages includes front ends for C (gcc), C++ (g++), Java (gcj), and Fortran (gFortran) intro.html

9 GCC Compile C code to an executable Compile C code to an executable gcc -o gcc -o Reporting all warning messages Reporting all warning messages gcc -Wall -o gcc -Wall -o

10 GCC (Cont’d) An example of compiling two.c files into an executable program An example of compiling two.c files into an executable program gcc -Wall -o assign1prob1 main.c list.c gcc -Wall -o assign1prob1 main.c list.c An example of compiling two files and then link them separately An example of compiling two files and then link them separately gcc -Wall -o main.o -c main.c gcc -Wall -o main.o -c main.c gcc -Wall -o list.o -c list.c gcc -Wall -o list.o -c list.c gcc -Wall -o assign1prob1 main.o list.o gcc -Wall -o assign1prob1 main.o list.o

11 Make command make automates the process of compiling a program make automates the process of compiling a program Makefile Makefile $ make $ make $ make clean $ make clean

12 Debugging gdb is GNU Debugger gdb is GNU Debugger A debugger for several languages Inspecting what the program is doing at a certain point during execution Errors like segmentation faults may be easier to find with the help of gdb /html_node/gdb_toc.html

13 GDB enable built-in debugging support enable built-in debugging support gcc [other flags] -g -o gcc [other flags] -g -o generating an expanded symbol table for use with gdb generating an expanded symbol table for use with gdb Example: gcc -Wall -Werror -ansi - pedantic-errors -g prog1.c -o prog1.x Example: gcc -Wall -Werror -ansi - pedantic-errors -g prog1.c -o prog1.x

14 GDB (Cont’d) enter gdb enter gdb gdb gdb enter gdb enter gdb quit quit printing line from a source file printing line from a source file list list running a program running a program run run breakpoint at a line number breakpoint at a line number break : break : break break break at a particular function break at a particular function break : break : set a breakpoint with condition set a breakpoint with condition break if break if deleting breakpoints deleting breakpoints delete delete proceed onto the next breakpoint proceed onto the next breakpoint continue continue Single step Single step step step

15 debugging exercise Reverse a string Reverse a string #include char * reverse(char s[]) { int c, i, j; For(i =0, j=strlen(s)-1; i< j; i++, j--) { c = s[i]; S[i] =s[j]; S[j]=c; } Main() { printf(“%s \n”,reverse(“database”)); }

16 GDB debugging exercise Program failed, why??? Load the program into GDB

17 GDB debugging exercise Here failed? What is the value of i

18 GDB debugging exercise Try the basic GDB commands here! Track your program step by step, inspect the variables..

19 Correct code #include char * reverse(char s[]) { int c, i, j; for(i =0, j=strlen(s)-1; i< j; i++, j--) { c = s[i]; s[i] =s[j]; s[j]=c; } return s; } int main() { char myStr[9]="database"; printf("%s \n",reverse(myStr)); return 0; }

20 From Java to C

21 Types, Operators and Expressions Data type Data type char, int, float, double, short int, long int Constants Constants #define PI Typedef: assigning alternative names to existing Typedef: assigning alternative names to existing typedef int myInteger; Relational and logical operators Relational and logical operators > >= < <= == != Increment and decrement operators Increment and decrement operators b = a++; b = ++a; b = a--; b = --a;

22 Control Flow The semicolon is a statement terminator The semicolon is a statement terminator If-Else, Else-If If-Else, Else-If if (expression) statement1 statement1 elseelse if (expression) statement2 statement2 else statement3 For loop For loop you need to define the counter variable before the loop for(expr1; expr2; expr3) statement While-Do While-Do expr1; While(expr2) statement expr3; Do-While Do-While do statement While(expression);

23 Control Flow (Cont’d) Switch Switch switch (expression){ case const-expr : statements default: statements } Conditional expressions (expr1 ? expr2 : expr3) Conditional expressions (expr1 ? expr2 : expr3) if(a>b) if(a>b) z=a;z = (a > b) ? a : b ; z=a;z = (a > b) ? a : b ; else else z=b; z=b;

24 Function declaration Return value Return value Default return value of a function in C is int Default return value of a function in C is int Java Java The use of function may appear earlier than its definition The use of function may appear earlier than its definition C program C program Should be declared somewhere earlier than their invocations Should be declared somewhere earlier than their invocations int power(int b, int e); … /* call power() here */ /* call power() here */… int power(int b, int e) { int r = 1; int r = 1; while (e-- > 0) r *= b; while (e-- > 0) r *= b; return r; return r; } int power(int b, int e) { int r = 1; int r = 1; while (e-- > 0) r *= b; while (e-- > 0) r *= b; return r; return r; }main(){... /* call power() here */ }

25 Input and Output printf(“the int value is %d”, var); printf(“the string value is %s”, var); printf(“the charactr and double values are %c and %e”, var); printf(“the double value is %e”, var); scanf(“enter an int: %d”, var); scanf(“enter a string: %s”, var); scanf(“enter a character and a double: %c %e”, var); scanf(“enter a string: %s”, var); Do not forget including

26 Variable scope int globalVar = 34; myFun(){ int x =1; } Global; outside of the function Local

27 Some details about C No boolean type in C No boolean type in C No explicit boolean type No explicit boolean type #define TRUE 1 #define TRUE 1 #define FALSE if (a){ #define FALSE if (a){ … } No function overloading in C No function overloading in C Two functions cannot have the same name Variables must be declared at the top of a basic block (for some c systems) Variables must be declared at the top of a basic block (for some c systems) The following may not pass the compiler { int a; printf("Hello world\n"); char b; } { int a; printf("Hello world\n"); char b; } Lack of exceptions Lack of exceptions Illegal activity may not be told (e.g. access memory that hasn’t been allocated in some way) No automated garbage collection in C No automated garbage collection in C you must free the memory

28 Standard library dynamic memory allocation dynamic memory allocation Input/output Input/output String handling String handling Mathematical functions Mathematical functions Characters Characters

29 Some common errors if (a=1){ if (a=1){ some stuff } some stuff } == Boolean evaluation = Variable assignment operator void myfunc(int a) { /*... */ } void myfunc(int a) { /*... */ } void myfunc(float b) { /*... */ } error: myfunc already defined

30 Exercise Write a program that Write a program that Accepts an input “x” (A value to progress up to) Accepts an input “x” (A value to progress up to) Starting at 0 and 1, outputs the Fibonacci sequence up to “x” permutations. Starting at 0 and 1, outputs the Fibonacci sequence up to “x” permutations. There should be two functions, for clarity. There should be two functions, for clarity. (main) Accepts the input and calls the fibonacci function. (main) Accepts the input and calls the fibonacci function. (fibonacci) One that accepts the value of x and outputs the sequence. (fibonacci) One that accepts the value of x and outputs the sequence.

31 Fibonacci in Java import java.io class Fibonacci { public static void main(String args[]) { System.out.println("How many numbers of the sequence would you like?"); InputStreamReader sr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(sr); try { String input = br.readLine(); int n = Integer.valueOf(input).intValue(); fibonacci(n); } catch (NumberFormatException e){System.out.println("That is not an integer. Please enter an integer value"); } catch (IOException e) { System.out.println("I did not recieve an input"); } } public static void fibonacci(int n){ int a=0,b=1; for (int i=0;i<n;i++){ System.out.println(a); a=a+b; b=a-b; }

32 Fibonacci in C #include int main () { int n; printf("\nHow many numbers of the sequence would you like?\n"); scanf("%d",&n); fibonacci(n); return 0; } int fibonacci(int n) { int a = 0; int b = 1; int sum; int i; for (i=0;i<n;i++) { printf("%d\n",a); sum = a + b; a = b; b = sum; } return 0; }