Objectives: After studying the Module 4 Game Skills 4, you will be able to:

1. Create a program using READ - DATA statements to enter sets of data.
2. Use INPUT statements as needed to make the program interactive.
3. Calculate the total sets of data and a the grand total.
4. Use LOCATE and PRINT USING to control the horizontal placement of numeric and string data in a table.

YOUR LESSON

Introduction

As you have seen, READ - DATA is the most efficient way to deal with sets of data within a program. And, PRINT USING and LOCATE are the best solutions for precisely controlling printing on the screen.

What else can we add to the programs you have written in Module 4? How about INPUT? Remember that INPUT allows you to create interactive programs.

Before you get confused about all of these programming techniques for getting data into variables, let's consider some general guidelines for when to use READ - DATA, INPUT, and LET.

• READ - DATA: This is a fairly easy decision. It is appropriate to use READ - DATA when you have sets of data that will not need to be changed during the course of a program.
• INPUT and LINE INPUT: This is another easy decision. When the program requires interactivity, you have no choice, you must use either INPUT or LINE INPUT. The LINE INPUT statement is a little more limiting than the INPUT statement, so the purpose of the program will dictate which one you use.
• LET: Well, another easy decision! Anytime you are going to perform a calculation, you must use an assignment (LET) statement. LET is also appropriate when you want to assign values to a few individual variables.

Was that easier than you thought? Those seem like some pretty simple general guidelines to follow; however, there are always exceptions! Here is a big one to consider.

If you had to process some kind of data (like a mailing list) for all of the students in a school, it would really clutter up a program to put all of the information in READ - DATA statements. Besides, addresses often change, so you would have to change the DATA statements in the program every time that happened. Consequently, READ - DATA would not be a good choice for such a program. This kind of situation is generally handled by storing data on a diskette or hard disk. When changes occur, the information on the storage medium is updated. When the information is needed, it is read into the program from the storage medium and used to perform the task. QBasic has the ability to read and write to storage media, but that is beyond the scope of this course.

On the other hand, sometimes you might be faced with the dilemma of whether to use LET or READ - DATA in a certain situation. After all, they basically accomplish the same thing--the assignment of data to variables. What's a programmer to do?

Maybe the easiest way to decide is based on the number of variables being assigned. Above, we discussed that it is appropriate to use LET when you want to assign values to a few individual variables. The key distinction here is few. If you had a program that required the assignment of "many" variables, you could either use a separate LET statement for each variable as we have been doing, or you could use a READ - DATA statement; however, it is hard to define what "many" would be. That is probably an individual decision that will be based on how much "clutter" you can stand in the program vs. how "well organized" you like your programs to be. When the "clutter factor" of using too many LET statements starts to detract from the program's organized appearance, it is probably time to switch to READ - DATA. (This is probably a good rule of thumb with regard to how well you keep your room at home picked up as well!)

Let's take a look at two quick examples and then tackle a new program.