Hour 1. Hands-On Programming

You have this book because you want to go farther than the typical computer user. You don’t just want to use computers; you want to write programs for them. You want the skills necessary to make computers do exactly what you want.

This 24-hour tutorial shows that you don’t have to be a wizard to become a proficient (or even an expert) programmer. By the time you finish this one-hour lesson, you will have entered your first computer program, run it, and looked at the results. This chapter springboards you into programming so you can get a feel for programming right away. Once you’ve had this hands-on experience, subsequent hours will explain more of the background you need to understand how to design and write programs.

The highlights of this hour include:

Learning what a program does

Understanding the truth behind common programming myths

Mastering source code concepts

Entering and running your first program

An introduction to the nature of programming

A hands-on practice with your first programming language

Most new programmers want to start programming right away. Yet, some background is necessary as well. This hour attempts to take care of both demands by offering an introductory background look at programming and then quickly jumping head-first into hands-on programming. If you went straight into a new programming language with absolutely no background first, you might miss the entire point of programming in the first place. So, the next few pages bring all readers up to a level playing field so that everyone who takes this 24-hour course can begin to write programs right away.

At its simplest level, a computer processes data. Figure 1.1 shows this as the primary goal of all computer programs. Many businesses call their computer programming departments data processing departments because computers process data into meaningful information. You may not have considered the difference between the words data and information before, but there is a tremendous difference to a computer professional. Raw data consists of facts and figures, such as hundreds of days of stock prices. A program might process that data into meaningful information, such as a line chart that shows the overall trend of the stock prices over time. It is the computer program that tells the computer what to do. Sometimes, a program might simply process data from another program without showing any output for the user. The processed data is still information because the program’s output, stored on the disk, is changed in some way. For example, a program that closes monthly account balances may collect data from various accounting systems in a company and combine, balance, and close that data, resetting the data for the following month.

A program is a list of detailed instructions that the computer carries out. The program is the driving force behind any job that a computer does. The computer cannot do anything without a program. It is the job of the programmer to design and write programs that direct the computer to take raw data and transform that data into meaningful information for the end-user. The end-user (usually just called the user) of the computer is generally the nontechnical, nonprogramming person who needs the results (the information) that the program provides.

You, as the programmer, are responsible for guiding the computer with the programs you write. Learning to program computers takes a while, but it is certainly rewarding. Computer programming offers the advantage of instant feedback, unlike a lot of other jobs you can train for.

Many misconceptions about computers exist and stem from a lack of understanding about how computers work and what computers are physically capable of doing. This book wants to shoot down the myths and improve your understanding of these machines. You’ll be programming computers in no time. The computer is nothing more than a tool that helps you do certain types of work. The computer itself is not bad or good. A hammer is a tool you can use for good (to build houses) or for bad (to break things). A computer in the wrong hands can be used for bad purposes, but that isn’t the computer’s fault any more than it is the hammer’s fault if someone misuses it.

The next three sections attack the three most popular computer myths. Have you heard any of them? Did you think some were true?

Not only can you be poor at math—you don’t even have to like math or have the desire to learn math to be a good computer programmer. The computer does all the math for you; that’s one of its jobs. There are countless expert computer programmers in the world who cannot tell you the area of a circle or the square root of 64. Relax if you thought this myth was reality.

Programming can provide beneficial side effects. It turns out that, as you become a better programmer, you may find your math skills improving. Developing programming skills tends to improve your overall capability for logical thinking, which underlies many skills in math as well. Therefore, being better in math might be a result of programming but it’s not a prerequisite.

Computers do not make mistakes—people make mistakes. If you have heard a bank teller tell you that $24 was incorrectly deleted from your savings account because “the computer program made an error,” the teller probably has no idea what really happened. People program computers, people run them, and people enter the data that the computer processes.

The odds of a computer randomly fouling up a customer’s bank balance are minute. Computers simply do not make random mistakes unless they are programmed incorrectly. Computers are finite machines; when given the same input, they always produce the same output. That is, computers always do the same things under the same conditions. Your job, as you learn to program, will be to reduce the chance of computer mistakes.

When a computer malfunctions, it does not make a simple mistake; rather, it really messes things up. When a computer fails, it typically breaks down completely, or a storage device breaks down, or the power goes out. Whatever happens, computers go all out when they have a problem and it is usually very obvious when they have a problem. The good news is that computers rarely have problems.

Before people invented computers, banks kept all their records on ledger cards. When a teller found a mistake (possibly one that the teller had made), do you think the teller said, “The ledger card made a mistake”? Absolutely not. Computers can have mechanical problems, but the likelihood of small mistakes, such as an incorrect balance once in a while, is just too small to consider. Such mistakes are made by the people entering the data or by (gulp) the programmers.

Of course, if you are reading this book, you want to learn enough about computers to write your own programs. Writing computer programs does take more work than using a microwave oven’s computerized timer functions. The work, however, primarily involves getting down to the computer’s level and learning what it expects.

Not only are computers getting easier to program every day, but you have more opportunities to learn about them than ever before. Cable television channels are loaded with educational shows about using and programming computers. Books and videos on the subject are all around you. The Internet itself contains scores of classes on all aspects of computers and other topics. There is probably a computer programming class now in session somewhere within 15 minutes of your house as you read this.

Hour 22’s lesson, “How Companies Program,” explores the chain of computer jobs and describes what each type of programming job is all about. If you are just starting out, you probably won’t be able to go to work as the most senior-level programmer, but you will be surprised at the salary your programming skills can bring you.

Businesses and individuals must factor in the cost of programs when making computer decisions. Whereas an individual usually buys a computer—called hardware because the machine isn’t changed often or easily—and is done with the hardware purchasing for a while, the purchasing of programs—the software—never seems to end, because software changes rapidly. As a future programmer, this is welcome news because you have a secure career. For the uninformed computer purchaser, the cost of software can be staggering.

A business must also factor in the on-staff and contract programmers and the time needed to write the programs it uses. More information on the programming and support staff appears in the next section.

Another advantage to JavaScript is that most programming languages need you to install an interpreter or compiler on your computer in order to execute your code. With JavaScript (and HTML), you only need a text editor. You type in your code, save it with an .html extension, and then open the saved file with your web browser.

A computer is only a machine. To give a machine instructions, your instructions might be fairly readable, as Figure 1.2’s are, but the code (another name for a program’s instructions) must be fairly rigid and conform to a predefined set of rules and regulations according to the programming language you use. Therefore, to write a program in the JavaScript programming language, you must conform to JavaScript’s rules of proper command spelling and placement. This programming language grammar is called syntax. (And you thought syntax was just a levy placed on cigarettes and liquor!)

Despite its name, JavaScript is not tied to the Java programming language (which is covered in Part III, “Object-Oriented Programming with Java,” of this book). In fact, the name has caused some confusion as computer fans thought that JavaScript was either an extension or spin-off of Java, but it got the name because Java was a hot new language at the time, and some thought the connection of the scripting language to the web development language would benefit the adoption and growth of JavaScript. Misleading name aside, the more you learn JavaScript, the more easily you will be able to learn additional programming languages. Although computer languages have different goals, syntaxes, and reasons for being, they are often similar in structure.

Listing 1.1 shows machine language. Can you decipher any of it? Your computer can. Your computer loves machine language. Actually, it’s the only language your computer understands. And different computers understand their own version of a machine language so what works on one type of computer will not necessarily work on another. It’s best to stay away from machine language and let products such as JavaScript convert your higher-level language into machine language’s cryptic 1’s and 0’s. To convert source code such as your JavaScript program to machine language, you need an interpreter (or for other languages, a compiler).

LISTING 1.1 Machine language is extremely difficult for people to decipher.

---

01100100
10111101
10010011
10010100
00001111
01010101
11111110

---

All programs you run on your computer, phone, or tablet, including Microsoft Word, Internet Explorer, and programming languages, are already converted into machine language. That’s why you can click a program’s icon and the program begins immediately. No interpretation or compilation is required. By providing you with the machine language only, software vendors serve two purposes:

1. They give you programs that execute quickly without the intervening compiling step.

2. They ensure that you don’t change the source code, thereby protecting their intellectual property.

1. Type a program’s source code and save it.

2. Load the code document, which is now an HTML document saved to your hard drive, with your web browser and see what happens.

3. If the page is not doing what you want and has errors, called bugs, you’ll need to fix those bugs in your source code and repeat these steps. Hour 7, “Debugging Tools,” explains how to locate and fix common bugs. You may need to do some bug hunting earlier than Hour 7 if you experience problems with your programs in these first few hours. If a program does not work as described, you will need to compare your source code very carefully to the code in the book and fix any discrepancies before saving it again.

You may be asking if there’s any difference between the slash and asterisk comment and the double-slash comments. Taking the second type first, the double-slash comment is known as a single-line comment. JavaScript will ignore all text to the right of the two slashes. As soon as you hit return, JavaScript will start paying attention to your code again. So if you want to keep commenting, you will need to start the next line with a fresh pair of slashes.

Click here to view code image

// The next five lines ask web visitors for their favorite
// color and Steinbeck novel

In the previous example, if you left off the two slashes, JavaScript would assume you were either typing color or calling a function named color and you might not get the results you were expecting.

When JavaScript encounters a comment that begins with the slash and asterisk, it will treat everything that follows as a comment until it sees a closing asterisk and slash (*/). This can be on the same line:

Click here to view code image

/* Next, the code calculates the area of the circle. */

Or it can go on for several lines:

Click here to view code image

/* This section is used to enter a contact
The user can enter a name, physical address,
up to 5 email addresses, home, work, and cell
phone numbers, and any additional comments
to help remember how they know the person. */

All languages support comments, which are also called remarks, although some languages use an apostrophe instead of the slashes. Although you’ll find many comments in programs, and you should put many comments in the programs you write, comments are not for the interpreter or for the computer. Comments are for people. In JavaScript, for example, the interpreter ignores all text to the right of the slashes or slash/asterisk. The computer knows that comments are for you and not for it.

Comments can identify programmers—If you develop programs with others or write programs for a company, you should put your name and contact information in comments at the top of your programs. Later, if someone has a question about the program or wants you to change the program, they’ll know that you wrote the program and they can locate you.

Before a section of tricky code, you can use comments to include your explanation of the code’s purpose. Later, if you or someone else needs to change the program, the change will be easier; reading the comments is much simpler than trying to figure out the goals of the tricky code from uncommented code.

Click here to view code image

if hours > 12          // Test the hour for AM/PM indicator
   hours = hours - 12  // Convert 24-hour time to 12-hour
   amOrPm$ = " PM"     // Set indicator that will print

Sure, as a programmer, you will often understand code without the need to put a remark to the right of each line. But at the time you write a program, the program is clearest to you. When you later go back to edit a program, what may have been clear before is no longer clear because time has passed. A few comments will go a long way toward reminding you of your original intent.

However, do not overdo comments. Some comments are redundant, as the following shows:

Click here to view code image

document.write("Martha");   // Prints the word Martha

Such a comment is not helpful and serves only to cloud an already-understandable instruction. Don’t overuse comments, but use them generously when needed to clarify your code.

You already got a taste of programming this hour by typing your first JavaScript program and opening the resulting document in your browser. As you saw by typing your own program into an editor, entering and running a code is not painful at all. As a matter of fact, the quick feedback that programming offers is a rewarding experience. Programmers often like their profession very much because they can see the results of their work quickly.

A. It is said that a program is written once and modified many times. Throughout this 24-hour tutorial, you will learn the importance of maintaining a program after it is written. As businesses change and computing environments improve, the programs that people use must improve as well. Companies provide upgrades to software as new features are needed. The programs that you write today will have to change in the future to keep up with the competition as well as with new features that your users require.

Q. Can I enter other programming language listings in my editor as well?

A. You can write programs in other programming language, such as C, C++, and Java, in your text editor. However, you would need a compiler or interpreter (depending on the language) to convert the programming language’s code to machine language. A machine language program is your program’s instructions compiled to a language your computer can understand.

2. What is a program?

3. What is a programming language?

4. True or false: Computers never make mistakes.

5. Why should people not fear the computer replacing their jobs?

6. What do programmers use editors for?

7. True or false: Java and JavaScript are related to each other.

8. What filename extension should you use when you create a JavaScript program?

9. True or False: There’s no problem writing your programs in your typical word-processing program.

10. Tweak the program in Listing 1.2 so the dialog box asks, “Who wrote this program?” and the answer the user gets upon clicking the button is your name.

2. A program is a set of detailed instructions that tells the computer what to do.

3. A programming language is a set of commands and grammar rules with which you write programs that give computers instructions.

4. False. A computer might make a mistake, but it’s rare that it does so. In the vast majority of cases where a computer is blamed, a person entered bad data or typed a bad program.

5. Computers increase jobs, not replace them. The information industry is one of the reasons for the past two decades of economic growth.

6. Programmers use editors to type programs into the computer.

7. False. JavaScript and Java only share a name; JavaScript was a scripting language that was developed at the same time Java was hot, so it was named in a way to take advantage of Java’s popularity.

8. If your code is going to stay in your HTML document, you can use .html or .htm, but when you create separate JavaScript files, use .js.

9. False. The default method of saving files in word processors will add formatting codes that will generate errors when you try to run your program. You can still use a word processor, but you must always remember to save your files as plain text.

10. Here is one possible solution:

Click here to view code image

<!DOCTYPE html>
<html>
<head>
<script>

/* This is the function that gets
called when the user clicks the
button on the main page */

function displayProgrammer()
{
document.write("Dean Miller did!");
}
</script>
</head>
<body>


<h1>My First Program</h1>
<p id="demo">Who wrote this program?.</p>

<button type="button" onclick="displayProgrammer()">And the answer is...</
button>

</body>
</html>