jjhusebo lab1 submission

ANSWERS.md

@@ -19,128 +19,226 @@ Please use [markdown](https://help.github.com/articles/markdown-basics) formatin
 
 Make another directory inside the `unixstuff` directory called `backups`
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `mkdir unixstuff/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:** *YOUR ANSWER HERE*
-
+**Answer:** ```
+	    cd backups
+	    cd ..
+	    pwd
+	    cd ..
+            cd ..
+	    pwd
+	    ls
+            cd
+	    ls
+	    ```
 ###Exercise 2a
 
 Create a backup of your `science.txt` file by copying it to a file called `science.bak`
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `cp science.txt science.bak`
 
 ###Exercise 2b
 
 Create a directory called `tempstuff` using `mkdir`, then remove it using the `rmdir` command.
 
-**Answer:** *YOUR ANSWER HERE*
-
+**Answer:** ```
+	    mkdir tempstuff
+            ls
+            rmdir tempstuff
+	    ls
+	    ```
 ###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:** *YOUR ANSWER HERE*
-
+**Answer:** ```
+	    cat > list2
+	    orange
+	    plum
+	    mango
+	    grapefruit
+	    cat list2
+	    ```
 ###Exercise 3b
 
 Using pipes, display all lines of `list1` and `list2` containing the letter 'p', and sort the result.
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `cat list1 list2 | grep p | sort`
 
 ###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:** *YOUR ANSWER HERE*
-
+**Answer:** ```
+	    chmod g-rw science.txt
+	    ls -l science.txt
+	    chmod g+w science.txt
+	    ls -l science.txt
+	    chmod g+r-w science.txt
+	    ls -l science.txt
+            chmod go-x backups
+	    ls -l 
+            chmod go+x backups
+	    ls -l
+	    ```
 ##Shell questions
 
 1. What option with the command `rm` is required to remove a directory?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `rm -dir`
 1. What is the command used to display the manual pages for any command?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** The `man` command
 1. What command will show the first 5 lines of an input file?
-  - **Answer:** *YOUR ANSWER HERE*
-1. What command can be used to rename a file?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `head -5 file`
+11. What command can be used to rename a file?
+  - **Answer:** `mv name name2`
 1. What option can we given to `ls` to show the hidden files?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `ls -a`
 1. What will the command `cat -n file` do?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** It will print the file with line numbers added.
 1. What will the command `echo -n hello` do?
-  - **Answer:** *YOUR ANSWER HERE*
-1. What command will display s list of the users who currently logged in in the system?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** display hello without the trailing newline.
+1. What command will display a list of the users who currently logged in in the system?
+  - **Answer:** `who`
 1. How do you change password on your account?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `passwd password`
 1. How can you list a file in reverse order?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `sort -r list`
 1. What does the `less` command do?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** Reads your input file, does not have to read the whole input file before starting.
 1. With `less` how do you navigate?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** By using key shortcuts (Like RETURN(one line forward or SPACE(one 		window forward)
+		Shortcuts are listed using `less --help`
 1. What command will display the running processes of the current user?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `ps`
 1. What command can be used to find the process(es) consuming the most CPU?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `top`
 
 ##vi questions
 1. How do we save a file in `vi` and continue working?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `:w`
 1. What command/key is used to start entering text?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** INSERT or `i`
 1. What are the different modes the editor can be in?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** COMMAND or INSERT
 1. What command can be used to place the cursor at the beginning of line 4?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `:4`
 1. What will `dd` command do (in command-mode)?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** At the cursor, delete the whole line.
 1. How do you undo the most recent changes?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** By pressing `u` in COMMAND mode.
 1. How do you move back one word?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** By pressing `b` in COMMAND mode
 
 ##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:** *YOUR ANSWER HERE*
+  - **Answer:** `gcc hello.c -c hello`
+		You cannot execute an .o file, and the compiler has not yet linked to the libraries.
 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:** *YOUR ANSWER HERE*
+  - **Answer:** Listing 2 you use the command `gcc hello.c -D DEBUG` to compile it in debug mode(you will get an exe named 		a.out), whilst if you issue `gcc hello.c -o hello` you will not.
+		Listing 3 will require you to change the variable in the hello.c file before you compile. You enable 				debugging by writing `gcc hello.c -D hello`
 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*
+  - **Answer:** Listing 2 Pros: Can be easily set in Debug mode at compile. Cons: Debug cannot be set progammaticly
+		Listing 3 Pros: Can be set automatically. Cons: Cannot be set at compile.
 1. Provide the command for generating the *map* file. Which of the `gcc` tools is responsible for producing a *map* file?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `gcc hello.c -o hello -Wl,Map=hello.map` The linker tool is responsible for producing the *map* file.
 1. What is the content of each of the sections in a *map* file. Explain briefly.
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** A link map provides information about the link, including the following: 
+Where object files are mapped into memory. How common symbols are allocated. All archive members included in the link, with a mention of the symbol which caused the archive member to be brought in.The values assigned to symbols.
 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:** *YOUR ANSWER HERE*
+  - **Answer:** ```
+		int datavar = 13;
+		int bssvar;
+		static const float rodatavar = 13.37;
+		```
 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:** *YOUR ANSWER HERE*
+  - **Answer:** For the double it uses `push, movsd, mulsd, leave and ret`
+		For the float it uses `push, movss, mulss, leave and ret`	
+		difference is that is uses different mov and mul instructions, because 		    	of the difference in the data type of the functions, float is 32-bit and double is 64.	
 1. How does `make` know if a file must be recompiled?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** File modification timestamp
 1. Provide a `make` command to use a file named `mymakefile` instead of the default `makefile`.
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `make -f mymakefile`
 1. How do you implement an *include guard*, and why is it needed?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** By implementing a test around the includes that checks if there might 		be multiple definitions when used in different files.
 
 ##Library Task
 
 Insert your code between the brackets `{}`:
 
-    void main( int argc, char *argv[] )
+	void main( int argc, char *argv[] )
 	{
-    }
+		int tab_size;
+	       	double min;
+		double max;
+
+		if (argc < 2)
+		{
+		printf("Please provide a table size.\n");
+		}
+ 		else if (argc == 3)
+		{
+        		printf("Please provide MAX value. Using default(0.0 - 100.0).\n");
+        		min = 0.0;
+        		max = 100.0;
+ 		}
+ 			else if (argc == 4)
+ 		{
+        		sscanf(argv[2], "%lf", &min);
+			sscanf(argv[3], "%lf", &max);
+ 		}
+ 		else if (argc > 4)
+ 		{
+        		printf("Too many arguments. Using default(0.0 - 100).\n");
+        		min = 0.0;
+        		max = 100.0;
+ 		}
+ 		else
+ 		{
+        		min = 0.0;
+        		max = 100.0;
+ 		}
+
+ 		sscanf(argv[1], "%d", &tab_size);
+ 		double table[tab_size];
+ 		srand(time(NULL));
+ 		int i;
+ 		for (i = 0; i < tab_size; i++)
+ 		{
+        		table[i] = ((double)rand()/INT_MAX) * (max - min  + 1) + min;
+		}
+
+ 		printf("Table: \n");
+ 		int j;
+ 		for (j = 0; j < tab_size; j++)
+        	{
+ 			printf("Element[%d] = %f\n", j, table[j]);
+ 		}
+
+ 		double sum;
+ 		sum = tab_sort_sum(table, tab_size);
+ 		printf("Sum:%f\n", sum);
+    	}
 
 	double tab_sort_sum( double *tab, int tab_size )
 	{
+	 	qsort(tab, tab_size, sizeof(double), cmpfunc);
+ 		int i;
+ 		double sum;
+ 		for(i = 0; i < tab_size; i++)
+ 		{
+        		sum += tab[i];
+ 		}
+ 		return sum;
 	}