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##Important Instructions

Please preserve the structure of this file, as it will subjected to partial automatic analysis. Only insert your answers by replacing the text YOUR ANSWER HERE; do not delete anything else.

Please use markdown formating to typeset code and Unix commands with the backtick character, for example, ls -la, or if you want to write code blocks, each line should be indented with four spaces, as done in the code below:

#include <stdio.h>

int main(void) {
	printf("Hello, world!\n");
	return 0;
}

##Exercises from the online Unix tutorial

###Exercise 1a

Make another directory inside the unixstuff directory called backups

Answer: mkdir backups

###Exercise 1b

Use the commands cd, ls and pwd to explore the file system.

(Remember, if you get lost, type cd by itself to return to your home-directory)

Answer: cd unixstuff/backups pwd: /home/stud/brynjulf/unixstuff/backups

###Exercise 2a

Create a backup of your science.txt file by copying it to a file called science.bak

Answer: cp science.txt science.bak .

###Exercise 2b

Create a directory called tempstuff using mkdir, then remove it using the rmdir command.

Answer: mkdir tempstuff rmdir tempstuff

###Exercise 3a

Using the above method, create another file called list2 containing the following fruit: orange, plum, mango, grapefruit. Read the contents of list2.

Answer: cat > list 2 orange plum mango grapefruit

###Exercise 3b

Using pipes, display all lines of list1 and list2 containing the letter 'p', and sort the result.

Answer: cat list1 list2 | grep p | sort plum grapefruit

###Exercise 5a

Try changing access permissions on the file science.txt and on the directory backups.

Use ls -l to check that the permissions have changed.

Answer: chmod go-rw science.txt chmod go-rwx backups

##Shell questions

  1. What option with the command rm is required to remove a directory?
  • Answer: dir
  1. What is the command used to display the manual pages for any command?
  • Answer: man
  1. What command will show the first 5 lines of an input file?
  • Answer: head -5 filename
  1. What command can be used to rename a file?
  • Answer: mv filename newfilename
  1. What option can we given to ls to show the hidden files?
  • Answer: -a
  1. What will the command cat -n file do?
  • Answer: output the lines with line numbers
  1. What will the command echo -n hello do?
  • Answer: displays hello before newline
  1. What command will display s list of the users who currently logged in in the system?
  • Answer: ls ~/..
  1. How do you change password on your account?
  • Answer: passwd
  1. How can you list a file in reverse order?
  • Answer: sort -r
  1. What does the less command do?
  • Answer: allows for faster reading/navigating in a file than vi would
  1. With less how do you navigate?
  • Answer: w - next window, z - previous window etc etc
  1. What command will display the running processes of the current user?
  • Answer: ps
  1. What command can be used to find the process(es) consuming the most CPU?
  • Answer: top

##vi questions

  1. How do we save a file in vi and continue working?
  • Answer: w
  1. What command/key is used to start entering text?
  • Answer: i
  1. What are the different modes the editor can be in?
  • Answer: insert, command
  1. What command can be used to place the cursor at the beginning of line 4?
  • Answer: :4 or :set 4
  1. What will dd command do (in command-mode)?
  • Answer: deletes the whole line at the cursor
  1. How do you undo the most recent changes?
  • Answer: u
  1. How do you move back one word?
  • Answer: b

##The C Language and Make tool Questions

  1. How do you use gcc to only produce the .o file? What is the difference between generating only the .o file, and building the hello executable done in the previous compilation above?
  • Answer: gcc -c hello.c -o hello.o ,the compiler creates an object file for each source file, before linking them together, into the final executable
  1. Give the command for compiling with debug enabled instead of normal compilation for the two examples shown in Listing 2 and Listing 3. Explain how to turn debugging on/off for the two cases.
  • Answer: Enabling debugging in listing 2 is done by passing -DDEBUG in command line, in listing 3 the debug is enabled at runtime
  1. Give a brief pros and cons discussion for the two methods to add debug code shown in Listing 2 and Listing 3.
  • Answer: YOUR ANSWER HERE
  1. Provide the command for generating the map file. Which of the gcc tools is responsible for producing a map file?
  • Answer: gcc file.c -Wl,-Map file.map, map link
  1. What is the content of each of the sections in a map file. Explain briefly.
  • Answer: .data = initialized, .bss = unitialized, .rodata = constants
  1. Rewrite hello.c to produce entries in the map file for .data, .bss, and .rodata. Hint: This can be done by adding one variable for each type to the file.
  • Answer: `int data = 5;``
  • 	`int bss;`

  • 	`const int rodata = 1;`
  1. Add the following function to hello.c: double multiply(double x1, double x2), which returns x1*x2. Use gcc to generate an assembly code listing for the program, and examine the assembly code. What assembly instructions are used to do this? Repeat this task, but now replace double with float. Explain!
  • Answer: pushq, movq, movss and muvss, float is 32-bit whereas double is 64-bit
  1. How does make know if a file must be recompiled?
  • Answer: It uses the makefile data base and the last-modification times of the files to determine if it needs to be recompiled
  1. Provide a make command to use a file named mymakefile instead of the default makefile.
  • Answer: make -f mymakefile
  1. How do you implement an include guard, and why is it needed?
  • Answer: #ifndef, used to avoid double inclusions

##Library Task

Insert your code between the brackets {}:

void main( int argc, char *argv[] )
{
}

double tab_sort_sum( double *tab, int tab_size )
{
}