Laboratory 0 (this is an optional lab)

Note that these lab notes for labs 1 to 5 were developed originally by Andrew Trigdell and then refined by Bob Edwards. Some minor modifications have also be made by myself (Eric McCreath).

This laboratory should take you less than 2 hours to complete. Make sure you ask your tutor for help if you get stuck. You are expected to print out and read through these instructions and to complete about 1 hour of preparation. This lab is mainly for people who would like a bit more C practice.

Learning Objective

The main objective of this lab is to gain some practice in writing C code. This includes:

• being able to do simple I/O,
• using simple flow control,
• memory allocation,
• understanding structures and pointers, and
• tracing system calls(ltrace and strace).

Preparation

Many people will have had some exposure to C and for those people this should be a straight-forward lab. However, if you have not done this before then you will need to do a lot more preparation. Also, remember to use the 'man' pages for detail about standard library routines.

Step 1

If possible it is helpful to get hold of an old C book. Any would do. Have a look through it and remind yourself of some C code. Also have a read through some C programs and familiarize yourself with the syntax (you could use the Linux kernel for this).

Step 2

Go through the steps of the lab and write out (on paper or in a text editor) the code for the problems given in the lab. This means that during the lab you can focus on debugging and running the programs.

During the Lab

Step 1 - Hello World!

Write a program that takes a list of names (each on a separate line) and says hello to each person. Input should come from stdin and output should go to stdout. So for example if I put my program in the file 'hello.c' I could have the following interaction with the program:

% gcc -Wall -o hello hello.c
% hello
Jim
Hello Jim!
Fred
Hello Fred!
^D
Bye

Optional Extra - If the program sees your name get it to say 'Hi' instead of 'Hello'.

Step 2 - marks list

Write a program that takes a list of names and marks. The program then prints out the following:

• the name of the person with the highest mark, and
• the names in reverse order.

Each entry (name and mark) should be stored in a struct. These structures should be linked together in a linked list (this will involve malloc and pointers!).

Now if an interaction should go something like this:

% gcc -Wall -o marks marks.c
% hello
Jim 10
Fred 13
Sue 20
Kate 12
^D
Sue has the highest mark.
The students are:
Kate 12
Sue 20
Fred 13
Jim 10

Step 3 - ltrace and strace

Run both ltrace and strace on each of your programs. What calls are made for I/O? Which calls are made for memory allocation?

Optional extra

Within the structure from step 2 add a pointer to a function which takes an integer as input and return an integer. When the data is read in, assign this pointer to either a routine that adds 3 to the number or subtracts 3 (alternate between these two). Now when you print the list of names and marks also show the mark with this function is applied.

The output from above should now be:

Sue has the highest mark.
The students are:
Kate 12 -> 9
Sue 20 -> 23
Fred 13 -> 10
Jim 10 -> 13