Mastering Visual Basic .NET

The Single data type can hold much larger values. Besides, the Single data type can also hold noninteger
values. I’m assuming you won’t ask for a loan of $25,000 and some cents, but if you want to
calculate the precise monthly payment for a debt you have accumulated, then you should be able to
specify a non-integer amount. In short, we should have declared the LoanAmount variable with the
Single data type in the first place (but then I wouldn’t have been able to demonstrate the overflow
exception).
An overflow error can’t be caught with data-validation code. There’s always a chance your calculations
will produce overflows or other types of math errors. Data validation isn’t going to help here;
you just don’t know the result before you carry out the calculations. We need something called error
handling, or error trapping. This is additional code than can handle errors after they occur. In effect, you’re
telling VB that it shouldn’t stop with an error message. This would be embarrassing for you and
wouldn’t help the user one bit. Instead, VB should detect the error and execute the proper statements
that will handle the error. Obviously, you must supply these statements, and you’ll see examples of
handling errors at runtime in the following section.
Building a Math Calculator
Our next application is more advanced, but not as advanced as it looks. It’s a math calculator with a
typical visual interface that demonstrates how Visual Basic can simplify the programming of fairly
advanced operations. If you haven’t tried it, you may think that writing an application such as this
one is way too complicated, but it isn’t. The MathCalculator application is shown in Figure 2.6, and
you’ll find it in this chapter’s folder on the CD. The application emulates the operation of a handheld
calculator and implements the basic arithmetic operations. It has the structure of a math calculator,
and you can easily expand it by adding more features. In fact, adding features like cosines and
logarithms is actually simpler than performing the basic arithmetic operations.
Figure 2.6
The Calculator
application window
BUILDING A MATH CALCULATOR
Designing the User Interface
The application’s interface is straightforward, but it takes quite a bit of effort. You must align buttons
on the form and make the calculator look as much like a hand-held calculator as possible. Start
a new project, the MathCalculator project, and name its main form CalculatorForm.
Designing the interface of the application isn’t trivial, because it’s made up of many buttons, all
perfectly aligned on the form. To simplify the design, follow these steps:
1. Select a font that you like for the form. All the Command buttons you’ll place on the form will
inherit this font. The MathCalculator application on the CD uses 10-point Verdana font.
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