# Strings and Classes

Welcome to PB161. If you haven't read the rules and guidelines in
Part A (directory ‹00› in the source bundle), please do so now,
before going on.

The exercises this week will look at some of the basics that you
have seen in the lecture: strings, dynamic arrays – ‹std::vector›,
classes with methods, and ‹const› references. These concepts are
further explored in the ‘demonstrations’ (commented examples; please
note that these do not replace the lectures – they are meant to be
complementary). The corresponding files in the source bundle are
named ‹d?_*.cpp›, i.e. ‹d1_fibonacci.cpp› through ‹d4_lemmings.cpp›.

 1. ‹fibonacci› – using ‹std::vector› (dynamic array)
 2. ‹hamming›   – introduction to ‹std::string›
 3. ‹hero›      – introduction to object composition
 4. ‹lemmings›  – collections of custom objects

The second part of the study materials for each week gives you a
couple of ‘elementary’ exercises, which you should be able to
quickly solve to make sure you understand the concepts from the
lecture and from the commented examples above. Sample solutions are
in Part S at the end of the PDF, or in the directory ‹sol› in the
source code bundle. Please note that the sample solution is not
always the simplest possible – it's fine to take a more roundabout
approach. The source files for this section are named ‹e?_*.cpp›.

This week, the elementary exercises are:

 1. ‹predicates› – properties of lists of numbers
 2. ‹palindrome› – checking that an ‹std::string› is a palindrome
 3. ‹pascal›     – fill in an ‹std::vector›

The next section has slightly more difficult exercises. These are
labelled «preparatory», since they exist to let you prepare for the
corresponding seminar. You are strongly encouraged to solve at least
3 of them every week (if you submit them by Saturday, you can then
gain a point for attending the seminar). The respective source files
in the bundle are called ‹p?_*.cpp›. «Note:» Discussing and sharing
solutions is strictly forbidden – you must solve the exercises on
your own. For details, see Part A (directory ‹00› in the source
bundle).

 1. ‹counting› – count words and lines in a string
 2. ‹fraction› – evaluate a continued fraction
 3. ‹words›    – break a string into a vector of one-word strings
 4. ‹account›  – encapsulation of state, ‹const› methods
 5. ‹shapes›   – object composition
 6. ‹contacts› – collections of your own objects

The last section has «regular» exercises – those will be (on
average) yet more difficult and let you further practice programming
with the concepts that you have learned this week. Like with
elementary exercises earlier, solutions to these can be freely
discussed and shared, you can work on the exercises with your
friends, and you can compare your solution to those included in
Part S. Some of these exercises will be solved interactively in the
seminar. The files are named ‹r?_*.cpp›.

 1. ‹wrap›    – wrap long lines into paragraphs of a given width
 2. ‹digits›  – representing numbers in a positional system
 3. ‹sieve›   – find prime numbers
 4. ‹bsearch› – binary search in a sorted ‹std::vector›
 5. ‹qsort›   – the staple of in-place sorting algorithms
 6. ‹radix› † – a fast comparison-free sorting algorithm

## a. Using the source bundle

We recommend that you work on ‹aisa›, which has all the required
tools installed and set up correctly. You can use ‹micro› as your
editor if you are not familiar with ‹vim›, or you can use a remote
editing feature in your code editor of choice. If you prefer to set
up your own, local, environment, you are of course free to do that,
but please keep in mind that your tools are your responsibility.

If you work on ‹aisa›, you can check your solutions against the test
cases provided with the exercises by running ‹make› (this tries to
compile all of them in order) or ‹make p1_counting› to compile and
test only one of them. Additionally, ‹make› will run your code
through ‹clang-tidy› and ‹valgrind›.

When you are satisfied with the solution, you can use ‹pb161 submit›
in the directory of the particular unit. This week, that's
‹~/pb161/01›. You can consult ‹pb161 status› to confirm that your
submission is in the system. Thus, the entire sequence looks like
this:

    $ pb161 update
    $ cd ~/pb161/01
    … edit code until tests pass / you are satisfied …
    $ pb161 submit
    $ pb161 status

You can see test results in the notepads in the IS. As an
alternative, you can use the following command to submit the
solution and display the test results as soon as they become
available:

    $ pb161 submit --wait