In part one of this series we covered making a basic “Hello World” plugin in Mono / C#. Today we are going to dive into different types of data, and how to define them. Show me part 1! Also if you thought part 1 was ugly, I added a new javascript syntax highlighter so I recommend you read it on my blog instead of planet.ubuntu.com.

Variables
A variable is something that stores a value. In different programming languages, these are handled differently. C# is called a static / strongly typed language as you have to tell it what variables are. To explain, I will use python in comparison:

Python Example

x = "This is a string"
y = 5

As you can see, we didn’t have to tell Python anything about what type of variables they are. In C# / Mono, we would do this like this:

C# Example

string x = "This is a string";
int y = 5;

I will tell you, after my years of development, that I program a ton of stuff in PHP / Python today. One of the worst and best parts of these languages is that they are dynamically typed. The fact that C# requires variables to be declared with a type before using makes life easier for testing and reading. There is a stack overflow post on what static typing gives you: Read the stack overflow post.

Variable Naming
Before we continue, you will notice in the top example I used the variable names x and y (to illustrate that the variable names really mean nothing to the compiler / interpreter. If I named them myString you might have been confused). If you do this in real life, I will find you and give you a thorough verbal lashing. I generally use camel case to name variables. Just do not abbreviate them as it really serves no purpose, and makes a lot of pain for people besides yourself maintaining code.

You can read about camel case at wikipedia.

The Source
For this program, I copied our HelloWorld.cs, and just modified it. I also have a modified makefile.

dataTypes.cs

using System;

// We create a class to contain it
class dataTypes
{
    static void Main(string[] args)
    {
        // The type 'bool' is always true or false
        bool isMonoTheOnlyPatentRisk = false;

        // To check if it is true or false in program code,
        // we can use an 'if statement'
        if(isMonoTheOnlyPatentRisk)
        {
            Console.WriteLine("isMonoTheOnlyPatentRisk was set to true");
        } else
        {
            Console.WriteLine("isMonoTheOnlyPatentRisk was set to false");
        }

        // Note how I named the variables -
        // lowercaseFirstThenCapitalizeEachWorld
        // this is called camel case -- I first read about it
        // in a Charles Petzold book, but I am sure it
        // probably didn't originate there.  Either way its
        // how I code, I recommend you name variables
        // as descriptive as possible. 

        // Note to only kids:  You will have the initial
        // reaction of saying: Why should I name stuff long?
        // That takes time and is stupid!
        // I used to be you 10 years ago, the problem is if
        // you need to use your code in several years of not
        // using it.  Your time will be completely wasted
        // figuring out what the heck is going on, despite
        // seeming so intuitive / easy to understand when you
        // did it

        // Integers store numbers
        int ourNumber = 5;

        // In most langauges we can evaluate these in
        // 'if statements' like bools above, but if we try in
        // C# this will fail.  In C# a bool can only be 0 for
        // false, 1 for true, or we can use the
        // Convert.ToBoolean function like this:
        if(Convert.ToBoolean(ourNumber))
        {
            Console.WriteLine("ourNumber was not 0!");
        } else
        {
            Console.WriteLine("ourNumber was 0");
        }

        // Lets see if we can compare this number
        if(ourNumber > 4)
        {
            Console.WriteLine("ourNumber was greater than 4");
        } else
        {
            Console.WriteLine("ourNumber was less than or equal to 4");
        }   

        // Make a string, and output it
        string helloWorldVariable = "Hello World!";
        Console.WriteLine(helloWorldVariable);
    }
}

Makefile

COMPILER=gmcs

all: helloWorld.exe dataTypes.exe

helloWorld.exe: helloWorld.cs
	$(COMPILER) helloWorld.cs

dataTypes.exe: dataTypes.cs
	$(COMPILER) dataTypes.cs
clean:
	rm -f helloWorld.exe dataTypes.exe

.PHONY: all clean

Output from our terminal

[sharms@sparrow mono]$ make
gmcs helloWorld.cs
gmcs dataTypes.cs
[sharms@sparrow mono]$ mono dataTypes.exe
isMonoTheOnlyPatentRisk was set to false
ourNumber was not 0!
ourNumber was greater than 4
Hello World!

Bonus Tip
Did you notice in the first part the way I named the bool? If you are programming, generally, your bool’s should start with ‘is’. This becomes very important once you start making complex ‘if statements’. Trust me on this one, it’s a habit you want.

Tags: Linux, mono, programming, ubuntu