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Category Archives for Programming

Dynamic Arrays in C – part 1

While working on my C programming skills I wrote a small program to simulate the functionality of dynamic arrays on other languages. That is arrays that grow as you add elements to them instead of having a fixed size. I decided that is has to be reusable and that you should be able to have multiple instances of them, so I structured my code with that in mind.

So this is the file structure:

  • main.c – initialize the array and fill it for testing purposes
  • array.h – function declarations
  • array.c – function definitons

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Sorting Java Collections

Java collections are most of the data structures that come with the language. They share the same basics methods thanks to the collection interface. One of the most common things you may want to do with a collection, besides adding and removing elements, is sorting them.

Let’s see an example with ArrayList
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PHP Arrays

This is an introduction to PHP arrays, so if you are new to the language or you just need a refresher you can get up to speed pretty fast.

This is how we initialize an empty array and add some elements to it:

Then we can see it’s contents using the print_r() function. You may want to put this between <pre> tags for better formatting.
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SQLite basics

SQLite is a serverless relational database. It is used notably by modern browsers like Chrome and Firefox to store data like history, cookies, saved passwords…

We are going to see how you can get around in the command line interface. To work with a database file you can start the program in this way:

What you get is a prompt similar to the mysql client. Now let’s see what tables are available:

If we want to see column names we can use the .schema command:

To customize the output format of query results you can use the .mode and .headers options, for example:

You can add these options to .sqliterc for permanent effect. Finally, if you want to exit just type .exit

-> Something annoying about sqlite is that the ALTER TABLE command is very limited. You can only rename a table or add a column, but you can’t modify or delete columns after they have been created. There is an official work-around for this, explained here: https://www.sqlite.org/lang_altertable.html

Using SQLite in Ruby: https://rubygems.org/gems/sqlite3

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Java: Regular Expressions

Regular expressions, regexp for short, allow us to build expressions for pattern matching. If you aren’t familiar with them you may want to check out some resources here.

In Java you can leverage the power of regexp using the pattern and matcher classes, you can import java.util.regex.* to make them available to your program. Let’s see some examples:

This is a simple method that takes in a pattern and a string to compare against and returns either true or false. We define patterns as strings, for example if we want to see if a word starts with any character but ends with “ello” we would call our method like this:

Which in this case will return true, as an alternative you could also use the String method startsWith()

Example of java regular expressions

Now lets say we want to find all words that match a certain pattern in a piece of text, rather than just comparing against a single word.

This method is a little more involved than the first one. First we need to compile our regexp and get a pattern object then we call the matcher method on our pattern object with the string we want to match against, and what we get is a matcher object which contains the results. Finally we loop over the results and print them to the screen.

Here is a possible call to our findWithPattern method.

For more details check the official documentation.