Variables

We can output text to the console, we can read input from the console with our program. What more could we possibly need?

Hopefully a lot more. And the concept of a variable will hopefully be evident after reading this article.

I will start by describing what a variable is. A variable is something in the program that holds a value. There are many ways of trying to explain this, with analogies or more direct.

The direct explanation is that the variable corresponds to an address in the computers memory range, that can hold the 0s and 1s that make up the value.

An analogy would be a post office locker that can hold an item, that would correspond to a value.

The basic idea of a variable is that the value it holds can change throughout the execution of the program.

Let’s consider a program without variables:

class Program
{
    static void Main(string[] args)
    {
        System.Console.WriteLine("Hello world!");
        System.Console.WriteLine("{0}", 42 * 42);
        System.Console.ReadKey();
    }
}

It’s not a bad program. It calculates the value of 42 * 42 (which is 1764). It’s deterministic, in that it will produce the same output every time it is run.

It lacks an important aspect though – it does not react to any input from the user.

It should be said that it could have been rewritten to act on the parameter args, what would be given as arguments to the command-line program. It would still be very limited in its scope without variables however.

Let’s introduce a variable into the equation.

class Program
{
    static void Main(string[] args)
    {
        string str = System.Console.ReadLine();
        try
        {
            int x = Convert.ToInt32(str);
            System.Console.WriteLine("{0}", x * x);
        }
        catch (Exception e)
        {
            System.Console.WriteLine("{0}", e.Message);
        }

        System.Console.ReadKey();
    }
}

So what is going on above? We read a string from the console, which means that we wait for the user to type something and hit return.

The string the user types is saved into a string variable. We try to convert the value of this variable into another variable x.

If the input is an integer, we display the square of this value.

That is a short introduction to variables. In the next tutorial we will look at different types of variables.