Summary

A program uses operators to manipulate variables, constants, and literal values to produce new results. The Visual Basic operators fall into five categories: arithmetic, concatenation, comparison, logical, and bitwise. In most cases, using operators is straightforward and intuitive.

Operator precedence determines the order in which Visual Basic applies operators when evaluating an expression. In cases where an expression’s operator precedence is unclear, add parentheses to make the order obvious. Even if you don’t change the way that Visual Basic handles the statement, you can make the code more understandable and avoid possibly time-consuming bugs.

The String data type has its own special needs. String manipulation plays a big role in many applications, so Visual Basic provides a StringBuilder class for manipulating strings more efficiently. On the one hand, if your program only works with a few short strings, it probably doesn’t need to use a StringBuilder, and using the String data type will probably make your code easier to understand. On the other hand, if your application builds enormous strings or concatenates a huge number of strings, you may be able to save a noticeable amount of time using the StringBuilder class.

The Date data type also behaves differently from other data types. The normal operators such as + and have different meanings than they do for other data types. For example, a Date minus a Date gives a TimeSpan, not another Date. These operations generally make sense if you think carefully about what dates and time spans are.

Just as addition, subtraction, and the other operators have special meaning for Dates and TimeSpans, you can use operator overloading to define operators for your classes. Defining division or exponentiation may not make much sense for Employees, Customer, or Orders, but in some cases custom operators can make your code more readable. For example, you might imagine the following statement adding an OrderItem to a CustomerOrder:

  the_order += new_item 

This chapter explains how to use operators to combine variables to calculate new results. A typical program may perform the same set of calculations many times for different variable values. Although you might be able to perform those calculations in a long series, the result would be cumbersome and hard to maintain. Chapter 6 explains how you can use subroutines and functions to break a program into manageable pieces that you can then reuse to make performing all of the calculations easier and more uniform.