Testing More than One Thing with Catch

In a modern piece of software, you wouldn’t have tests for just one class.  You’d have exhaustive tests for all the functionality in your program.  However, it would be challenging to put all of the tests in one single tests.cpp file.   [Read more…]

Spring 2018 Data Structures Prep

It is no secret that CSE 2341 – Data Structures – is a very demanding course.   The course requires a great deal of dedication and perseverance.  I have received a few requests about what to do over winter break in terms of review and prep.  This blog post has some suggestions and links to possibly useful info.

[Read more…]

Binary Trees and Binary Search Trees

Trees are a very important data structure, especially binary trees and its variants.  Please watch the videos linked below to get up to speed on Trees, Binary Trees, Binary Search Trees.

 

B+ Trees

B+ Trees are very efficient search tree data structures that are related to binary search trees.  They are particularly useful in indexing situations where the entire data set cannot fit into main memory at one time.  Each node in a B+ Tree contains multiple keys and pointers (as compared to 1 key and two pointers in a binary search tree).   [Read more…]

Binary Trees

Binary trees are a very fundamental data structure in computer science.  As you continue to learn and explore in different sub-domains of CS, you’ll see them pop up quite frequently.  Here are some things you should Binary Trees and their cousins.

  • General Binary Trees
    • Pre -, In -, and Post-order traversals
    • The height (or depth) of a tree
    • Different node terminology (leaf, level, ancestor, descendant, etc.)
    • Some info to peruse
  • Binary Search Trees
    • Remember, binary search trees are binary trees that also conform to the binary search property: all values in the left subtree of a node are smaller and all values in the right subtree of a node are larger (duplicates not withstanding)
    • Some algorithms you should think about w.r.t. bin search trees:
      • inserting a new value
      • searching for a value
      • deleting a value from the tree
      • determining the height of the tree
      • determining if a binary tree is indeed a binary search tree
      • what’s the most efficient way to create a copy of a binary search tree?
      • what’s the best way to destroy (delete all nodes) a binary search tree?
    • Some info to peruse
      • David Eck link above
      • Cliff Shaffer’s Data Structures and Algorithms book linked above Section 5.4 starting on page 168.
  • AVL Tree – a Self Balancing Binary Search Tree
    • AVL Balance Property: for every node n in an AVL tree, the height of the left subtree and the height of the right subtree may differ by no more than 1.
    • Some info to peruse

Lists, Stacks, and Queues

Lists, stacks, and queues are some of the most fundamental data structures to computer science.  Below are some links to information you may find helpful as you explore these data structures:

There are plenty of videos on Youtube about these topics as well. Check them out.

C++ and Catch – Adding your Own Main Method

When you begin coding on a project, it is perfectly acceptable and even advisable to allow the Catch library to generate the main method for you.  That is what the #define CATCH_CONFIG_MAIN (very first line in the tests.cpp file)  directive tells Catch to do.

As you transition from implementing the data structures to implementing a higher-level project, you will want to eventually create your own main method.  Here is how to transition to using your own main without getting rid of tests and testing.

In QtCreator, follow these steps

  1. Add a new cpp file to your project that will contain your main driver.  If you still have the original main.cpp that was added when you created the project, that is fine to use as well; make sure it is listed in the project explorer on the left side of the code window.
  2. Comment out#define CATCH_CONFIG_MAIN at the top of the tests.cpp file.  This will tell the Catch library NOT to generate its own main method.
  3. In your main driver file, copy and paste the following code (to start with). Read the comments throughout to help you understand what is going on.
//CATCH_CONFIG_RUNNER tells the catch library that this 
//project will now explicitly call for the tests to be run. 
#define CATCH_CONFIG_RUNNER
#include "catch.hpp"

//A macro used in main to determine if you want to run
//the tests or not. If you don't want to run your tests,
//change true to false in the line below.
#define TEST true

/*
* runCatchTests will cause Catch to go ahead and
* run your tests (that are contained in the tests.cpp file.
* to do that, it needs access to the command line
* args - argc and argv. It returns an integer that
* ultimately gets passed back up to the operating system.
* See the if statement at the top of main for
* a better overview.
*/
int runCatchTests(int argc, char* const argv[])
{
    //This line of code causes the Catch library to 
    //run the tests in the project. 
    return Catch::Session().run(argc, argv);
}

int main( int argc, char* const argv[] )
{
    //If the TEST macro is defined to be true,
    //runCatchTests will be called and immediately
    //return causing the program to terminate. Change TEST
    //to false in the macro def at the top of this file
    //to skip tests and run the rest of your code.
    if (TEST)
    {
        return runCatchTests(argc, argv);
    }

    //start working on other parts of your project here.
    return 0;
}

Once you’ve added that code, rebuild your project (Build menu| Rebuild All) then execute your project.  Your tests should run as normal.

Let’s Review Pointers

Pointers cause a lot of heartburn among students.  Hopefully this post will address some or all of the things you may be struggling with in the world of pointers.

For pointers to make sense, particularly the parts of them that are important for this class, you need to remember a few fundamental pieces of information:

  • Each location where data can be stored has an address.
    • Analogy: Every post office box in Hughes Trigg has an individual address.  If each didn’t, then the workers wouldn’t know what mail goes in which box.
    • Note that even pointers have addresses.  So, if I have [Read more…]

Memory Diagrams

The fact that c++ allows programmers to manage memory directly is one of its great strengths. It is also something that can lead to a ton of tough debugging and hair-pulling.  There are quite a few “things” a programmer can use to avoid most of these problems, but it is important to understand what’s going on under the hood of C++ so that you can fully understand why those other libraries are useful.

Memory Diagrams can help you not only learn the ins and outs of memory management, but they can also help in a debugging situation as well.  A memory diagram is a drawing that represents the state of the memory used by a program at a particular point in execution.  Of course, it is an abstraction of the actual memory usage, but contains enough detail to be very useful.

A memory diagram usually contains two major sections: 1) stack memory, and 2) heap memory.  These two are usually split between the left and the right on a piece of paper. Here is a template you can have a look at:  Memory Diagram Template.

Here is a link to a screencast on Vimeo I made a couple semesters ago related to drawing memory diagrams.  We’ll also be going over them in class as we talk about memory management.

Some related help:

  • Eric Roberts’ (Stanford) Heap-Stack DiagramsHandout on Heap-Stack Diagrams from their Lab sections (This is a link to some of the PDFs saved in Evernote) – These diagrams are quite a bit more “low level” than the method I use, but the general idea is the same.  The memory diagrams start at Problem 3.  A pdf of the solutions is included as well.
  • Debugging Software Crashes II – quite detailed, but a good resource for understanding memory.

Prep for Data Structures

Data structures is a challenging course.  I routinely receive requests for information about how to prepare for the course or what material to review.  Generally speaking, the most important thing to do is review and get comfortable with C++ and problem solving using C++.  Some of the topics that are of particular importance are:

  • Developing algorithms using fundamental control structures
  • Problem decomposition (breaking a problem down into steps to solve it)
  • Object oriented programming in C++ (classes, inheritance, and polymorphism in c++)
  • Pointers (what they are, how to use them, etc.) including pointers to pointers and arrays of pointers
  • Relationship between pointers and arrays
  • Memory management is a biggie, so I’ll break it down into finer points
    • Dynamic Memory Allocation and deallocation (new, new[], delete, and delete[])
    • What methods you should explicitly include in a class that contains dynamic memory (copy c’tor, overloaded operator =, destructor)
    • Difference between stack and heap (free store)

I don’t expect you to be an expert in all of the topics above, but I would expect that you’ve heard of all of them.  And, at least for some of them, you’ve got a firm understanding of what they are/mean/are used for.

Here are some links to materials from the last time I taught CSE 1342 that you might find useful:

If you’d like any more info on a particular topic, feel free to drop me an email.