This document is created as a handout of my workshop at Péter András Gimnázium for Erasmus high school teachers. The aim is to get a grasp of basic programming concepts in a trending paradigm and technology stack what they could pass on to their students across many countries in Europe.
- Table of Contents
- Introduction
- Learn Concepts By Examples
- Applications With Graphical User Interfaces
One of the first computer science models is Alan Turing's "automatic machine", lately called "Turing machine" (by Alonzo Church). These machines operate with sequentially readable and writable machine tapes. The machines themselves represent their programs, their "configurations". These configurations define state transitions on certain inputs (read from tape).
The next big iteration is the Random Access Machine (RAM machines) which uses registers instead of tapes. Harvard architecture stores program and data separated, while John von Neumann, Hungarian mathematician created his architecture as a review of EDVAC. His architecture stores both program and data in RAM memory, this is the so-called stored-program principle on which computers (including smartphones, smart watches, smart refrigerators, etc) we have Today are based on.
At first, programmers wrote machine codes directly, actual sequences of ones and zeroes, which had proven to be hard to read by human eyes, and easy to make mistakes in. This situation generated the demand for new tools for programming computers -- generating machine code -- which helps association.
Assembly is a programming language which eases association between source code -- created by programmers -- and actual machine code which is to be executed. Assembly directly maps machine (CPU) instructions and register names. An Assembly compiler -- which creates machine code from source code written in Assembly language -- is called an assembler. The following snippet stores integer number 5 and 7 in registry eax and ebx, then calculates their sum, stored in eax.
mov eax 5
mov ebx 7
add eax ebxProgramming languages which introduce further abstractions -- diverging from 1:1 representation of CPU command set -- are called higher-order programming languages.
Programming languages can be categorised in multiple ways by multiple properties like paradigms, support of different language constructions, but one of the main dividers is the fact if they are compiled languages or interpreted ones?
Compiled languages are using compilers to generate executable programs. Compiled languages tend to be strictly-typed, and in general, their executables have better performance than interpreted languages, implementing the same computations. Few example of compiled languages: C, C++, Fortran, Swift.
Interpreted languages are using interpreters to execute source code (text form) written in their programming language. Interpreters work by interpreting source code line-by-line as execution goes. Interpreted languages are useful because their portability and ease of modification, this is why it is popular among scripting languages, like Bash, Python, JavaScript.
Interesting fact about JavaScript: It has been born to be interpreted by web browsers, handling dynamic content and basic interactions. Today all mainstream web browsers support JavaScript as part of their base functionality. JavaScript is actively developed with it's standard, ECMAScript, by it's standard committee. JavaScript lives it's renaissance with the emerge of single page web applications, such as Facebook (the webpage), Twitter, even Microsoft Teams and GMail, Google Hangouts, etc.
Hybrids are those programming languages which can be both interpreted and compiled as well. Such language is Haskell, a pure functional programming language. Another type of Hybrid languages are those languages which are being compiled not directly into machine code (binary), but into so-called "byte code", which by itself cannot be executed, only interpretable by Vritual Machines. These Virtual machines, like Java Virtual Machine or .Net Frameworks exist to serve as a layer between their own type of byte code and the virtual machine itself. These virtual machines are implemented on multiple Operating Systems on multiple hardware architectures, so a source code compiled only once, can be executed on multiple environments. These languages take benefits of having their compiler (static analysis, strong type-systems, optimalisation) and the portability of interpreted languages. Their performance is somewhere in between the 2 main category. Their byte code is generated for the VM itself, uses lower-level abstractions then the source language, using VM command set, and easier to parse).
Our programming language of choice in the following sections is C#, because it introduces the basics for beginners in a type-safe environment, while supports most of the modern program language concepts for those who are willing to learn how to express their computations in more expressive and safe ways. Also C# is used widely in the industry from web services, mobile applications through artificial intelligence to game developments. Available on multiple platforms. However, for our graphical application examples later on Windows is a requirement. With a bit of learning other frameworks (like Xamarin) can be used to achieve the same results on them. Choice is made respecting availability of Windows in classrooms across Europe.
Let's create our first commandline application in Visual Studio:
- Start Visual Studio
- Click New Console Application
- Name it "Hello World" and save it
- Click "Build and run"
Since the whole architecture of computers and the bases of computer science are born of Turing Machines, and by their "step-by-step" analogy, the most trending paradigm is imperative paradigm when we discuss algorithms at their core concepts. Imperative style uses the term "state" which by name refers to the state of the computer, or in our case the program. A single dimensional projection of state is a variable, which stores a single value. On the other way around our initial (and adequate on introduction level) definition of state is the conjunction of all of our variables with their values in the moment of observing.
C# combines statements into sequences by listing commands. Each command is terminated with a semicolon.
Console.WriteLine("Hello!");
Console.WriteLine("How are you?");- Create a program, which declares a string variable,
- Ask users name, (awaits input to variable)
- Greets user by name
With the introduction of "if" (conditional execution) C# is able to handle alternatives.
Forms of if
int a = 6;
if (a < 4) {
Console.WriteLine("a is lesser than 4");
}
Console.WriteLine("Hello!");If-Else
int a = 6;
if (a < 4) {
Console.WriteLine("a is lesser than 4");
} else {
Console.WriteLine("a is greater or equal than 4");
}
Console.WriteLine("Hello!");Else-If
int a = 6;
if (a < 4) {
Console.WriteLine("a is lesser than 4");
} else if (a == 4) {
Console.WriteLine("a equals 4");
} else {
Console.WriteLine("a is greater than 4");
}
Console.WriteLine("Hello!");- Create a program which tells if given integer input is equal.
- Create the same program using different if structure.
For "counter" loop
for (int i = 0; i < 5; i++)
{
Console.WriteLine(i);
}While "pre-tester" loop
Note: A a post-tester alternative, do-while can be used.
int i = 0;
while (i < 5)
{
Console.WriteLine(i);
i++;
}Write a program which reads input until guess is correct
Note: Binary search or half-interval can be introduced with this example.
Structure your previous solutions into functions and procedures.
When to use functions? When to use procedures?
Create a guess game manager with private stored number and public CheckGuess logical function.
Create Car interface with
- TopSpeed property
- Start procesure
- Stop procedure
- Accelerate procedure
- Brake procedure
Implement Car interface with DieselCar and ElectricCar classes
Create GUI application with a single button which "jumps" to other position on mouse hover.
Implement the same guess game as a GUI app, using text box and buttons and labels.
Note: guess game manager is reusable on this excercise.
Create an application which can calculate speed, distance and time (in case two of them is already given).
Generate an n times m game board of buttons, implement the classic memory game!