Every program, no matter how complex, can be reduced to five fundamental steps. These steps are
Let's examine each of these steps in greater detail.
The initialization step is the first step you should think about when you design a program. The initialization step includes everything the program should do before the program begins interacting with the user. At first, the concept of doing things before interacting with the user might seem strange , but you've probably seen many programs that do exactly the same thing.
For example, we've all used Microsoft's Word, Excel, or similar programs. With such programs, you know that you can click on the File menu option and see a list of the files you worked with recently near the bottom of the menu. They didn't get there by magic. The program probably read the list of recently used files from a disk data file and appended that list to the File menu. Because this list is read before the program displays anything to the user, it falls under our Initialization step.
Anther common task that's often relegated to the Initialization step includes reading setup files. Such setup files might include information about the path names where certain database or other disk files can be found. Depending on the type of program being run, setup files might also contain information about display fonts, printer names and locations, foreground and background colors, screen resolution, and similar information. Other programs might read information about network connections, Internet access and security privileges, passwords, and other sensitive information.
In your own programs, you need to think about what type of information your program must have before it can do its job. If your design requires any type of setup or pre-program information, the Initialization step is probably where you should handle it.
The Input step is exactly what you expect it to be. It's the step that collects whatever inputs the program needs to accomplish its task. In most cases, if you think about what the program is supposed to accomplish, defining the list of inputs is fairly simple. For example, if you're writing a loan interest program, you know you'll need to ask the user for the amount of the loan, the interest rate, and the length of the loan.
In other cases, however, you really need to think about what inputs should be requested of the user. For example, if you're writing an address book program, do you really want to ask the user to type in the name of the disk file that holds the address book and the location of that file each time you run the program? In other words, some of the Input step can, and properly should, be pushed into the Initialization step. The exact nature of amount of information that can be read in the Initialization step depends on the nature of the program. However, as a general rule of thumb, most users would like repetitive information stored in a setup or initialization file rather than re-entering it each time they run the program.
Where the inputs come from is a design decision. Setup files are great and should be used whenever possible. Obviously, other input information cannot be known until the user types it in, as in our loan interest example. In such situations, you'll likely use text boxes to collect the information from the user for use in the program. Because the user must interact with these text boxes to supply program information, the way you lay out the text box, labels, menus , and other program elements defines an important element of the user interface for the program.
Entire books have been written on how to design an effective user interface. There's no way that I can do the topic justice right now. However, it never hurts to keep in mind that a lot of people in the world read from left to right, top to bottom. If you expect the user to skip around all over the screen filing in a bunch of randomly placed text boxes, chances are that the user's going to be a little miffed. I'll have a lot more to say about the design of a user interface as we progress through the text.
The Processing step involves acting on the inputs to produce the result desired from the program. In our loan example, the program would accept the inputs (that is, the loan amount, interest rate, and term of the loan), plug them into a financial equation, and solve the equation to yield the desired result (that is, a monthly payment amount). Stated differently, the Processing step accepts the inputs, "crunches" them, and produces an answer to the problem.
Note that the Processing step usually does not display anything on the screen. Its sole purpose is to act on the data to generate a result. There's one notable exception to this rule, however. If you know beforehand that the Processing step is going to take a long time, it's usually a good idea to provide some feedback to the user that the program is still running. We've all run programs where a progress bar shows us what percentage of the task at hand has been completed. Another common example is programs that provide an estimate of the time remaining before completion. A lot of Web-based program use this approach. These situations need some form of feedback so that the user knows the program is still working. However, in situations in which the Processing step is fairly quick, displaying information to the user normally isn't done.
In a sense, this is the whole purpose of the program in the first place: to give the users an answer to whatever problem it was they wanted solved . Many of our sample programs display an answer in a single text box. If, for example, you wrote a program to calculate a monthly loan payment, just displaying the payment in a text box is all that the Output step needs to do.
Other programs, however, are much more complex. Perhaps you've run programs that read your name, address, phone number, and perhaps a half- dozen other pieces of information from a database and then display them on the screen. Such complex programs might need several dozens of text boxes to display the necessary output information. In some situations, displaying the results cannot be done efficiently in text boxes. For example, displaying a table filled with customer data might better be done with a grid control or a list box that the program fills in as needed.
The important thing to note in the Output step is that because you're displaying results to the user, it's also part of the user interface. You saw earlier that the Input step was an element in the user interface because it collected data from the user. In the Output step, the user interface interacts with the user in a more passive manner, but still needs to consider the needs of the user in the design. Presenting information in an informative manner is almost an art form. I'll have more to say about Output step considerations as we get into more complex programs in later chapters.
The Cleanup step is used to gracefully shut down a program after it has completed its task. You can think of this step as the counterpart to the Initialization step. Although many simple programs can simply end without any further work by the programmer, more complex programs might need some help. For example, if your program reads a setup file to initialize some variables during the Initialization step, the Cleanup step probably should update those variables in the setup file with the user's latest information.
The Cleanup step is often associated with closing disk data files, including setup and database files. Some programs track how long a user ran a program and writes that information to what's called a log file. It isn't uncommon for log files to track the name of the people who were running the program, the dates and times they started running the program, and when they stopped using the program.
Another type of log file is called an error log file. The purpose of an error log file is to record information about any errors that were encountered as the program ran. Programmers can use the content of the error log file to help them debug the program should the need arise.
The actual tasks that are performed in the Cleanup step depend on the needs of the program itself. However, chances are that if something needs to be done in the Initialization step, some form of matching tasks is likely needed in the Cleanup step. Opening and closing different types of disk files is a common task for these two steps.
Five Steps for Every Program?
Does every program require all five programming steps? No. As you'll see in the next few chapters, we have a number of sample programs that don't need the Initialization or Cleanup steps. The sample programs are so simple that there's no need for these two steps. Normally, the Initialization and Cleanup steps appear in the design as the complexity of the program increases .
As you gain experience in writing programs, you'll develop a knack for knowing which programs need all five programming steps and which don't. However, you should always approach a programming design problem under the assumption that all five steps are needed. It's always easier to throw away steps later in the design than it is to squeeze them in once the design is well underway.