What is programming?

Data and information

Now that you understand computers as machines that process data and that programs tell computers what to do with the data, let’s delve a little bit deeper into the nature of data and information. People use the words data and information interchangeably, but I think it’s important to make a distinction between the two because the way that computers and humans consider data is completely different. Take a look at Figure 2-7.

Figure 2-7 Data on the left; information on the right.

The two items in the figure contain exactly the same data, except that the image on the left is closer to how the document would be stored in a computer. The computer uses a numeric value to represent each letter and space in the text. If you work through the values, you can figure out what each of them are, starting with the value 87, which represents an uppercase W.

Because of the way that computers hold data, another layer sits underneath the mapping of numbers to letters. Each number is held by the computer as a unique pattern of on and off signals, or 1s and 0s. In the realm of computing, each 1 or 0 is known as a bit. (For a wonderful explanation of how computers operate at this level and of how these workings form the basis for all coding, see Charles Petzold’s Code: The Hidden Language of Computer Hardware and Software.) The value 87, which we know means “uppercase W,” is held as the following bit pattern:

1010111

I don’t really have the space to go into precisely how this works (and Charles Petzold already did this!), but you can think of this bit pattern as meaning “87 is made up of a 1 plus a 2 plus a 4 plus a 16 plus a 64.”

Each of the bits in the pattern tells the computer hardware whether a particular power of two is present. Don’t worry too much if you don’t fully understand this, but do remember that as far as the computer is concerned, data is a collection of 1s and 0s that computers store and manipulate. That’s data.

Information, on the other hand, is the interpretation of data by people to mean something. Strictly speaking, computers process data and humans work on information. As an example, the computer could hold the following bit pattern somewhere in memory:

11111111 11111111 11111111 00000000

You could regard this as meaning “You are $256 overdrawn at the bank” or “You are 256 feet below the surface of the ground” or “Eight of the thirty-two light switches are off.” The transition from data to information is usually made when a human reads the output.

So why am I being so pedantic? Because it is vital to remember that a computer does not “know” what the data it is processing actually means. As far as the computer is concerned, data is just patterns of bits; it is the user who gives meaning to these patterns. Remember this when you get a bank statement that says that you have $8,388,608 in your account!

Code Analysis: Mystery program investigations

You are now going to run another mystery program to take a look at how data is stored in a computer. This program has the rather unoriginal name of Ch02_02_MysteryProgram2. You can select and run it by using the same steps as before. (You can also use Visual Studio to look at the code right at the start if you like, but I’d call that cheating.)

When you run the program, you’re asked to enter something. Type the word hello, select the Enter key, and the program displays what you see here:

Click to view larger image

The program displays the word you just typed in, followed by a list of mysterious codes. If you look carefully, you can start to work out what the codes mean. The program displays five code values, which is the same number of letters contained in the word “hello.” What’s more, the third and fourth codes are the same number, just like in “hello,” in which the third and fourth letters are the same.

It turns out that these “codes” are actually the numbers that are used by your computer to represent those letters of text. Modern digital devices use a standard called Unicode that provides a mapping of character codes to particular numeric values. This mystery program just takes each character in the word you type in, converts it to a number, and then displays the number. Let’s take a look at exactly how it works by analyzing the code.

public class Ch02_02_MysteryProgram2
{
    public void StartProgram()
    {
        SnapsEngine.SetTitleString("Mystery Program 2");

        // Read a string from the user
        string inputText = SnapsEngine.ReadString("Enter something please");

        // Only display the first 10 characters from the string
        if (inputText.Length > 10)
            inputText = inputText.Substring(0, 10);

        SnapsEngine.AddLineToDisplay(inputText);

        // Get each character in the string
        foreach (char ch in inputText)
        {
            // Get the number that represents this character and
            // display it
            int chVal = (int)ch;
            SnapsEngine.AddLineToDisplay("code = " + chVal);
        }
    }
}

This is a more complex program than the first mystery program. It contains a loop—a kind of programming device that lets a program repeat an instruction—that is applied to each character in the word you type, converting the character to an integer and then displaying it. There are some quite advanced C# constructions used in this code, which we will get to later in the book, but you should be able to pull out some elements that make sense. And for the moment, that’s enough.

Programmer’s Point: It is useful to be able to “read” program code

Over the years I’ve looked at a great many programs. Some were programs that I wrote, and some were written by other people. Some programs were written by using a programming language that I know, while others were written in a language I’d never seen before.

I’ve learned not to be distracted by the bits of the program I don’t understand yet and to focus on the parts that make sense to me. You might not know what the public class bit of the program listing means, but the line string inputText = SnapsEngine.ReadString("Enter something please"); should kind of make sense and leave you thinking this might be where the program gets a string of text.

Americans use the term “spelunking” to describe the hobby of exploring underground caves. The term is also used to describe the “hobby” of exploring unfamiliar program code. You should try to get good at spelunking the programs in this book. You can start by looking for landmarks that you know are there and then work from those, refining your understanding of the program’s behaviors. For example, you know that somewhere in the program it performs an action for each character in the string. Knowing that, you should be able to work out where in the code this action happens.