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Efficient Use of Data Types

Undeclared variables and variables declared without a data type are assigned the Object data type. This makes it easy to write programs quickly, but it can cause them to execute more slowly.

Specifying data types for all your variables is known as strong typing. Using strong typing has several advantages:

  • It enables IntelliSense® support for your variables. This allows you to see their properties and other members as you type in the code.

  • It takes advantage of compiler type checking. This catches statements that can fail at run time due to errors such as overflow. It also catches calls to methods on objects that do not support them.

  • It results in faster execution of your code.

For variables that never contain fractions, the integral data types are more efficient than the nonintegral types. In Visual Basic, Integer and UInteger are the most efficient numeric types.

For fractional numbers, Double is the most efficient data type, because the processors on current platforms perform floating-point operations in double precision. However, operations with Double are not as fast as with the integral types such as Integer.

Use the Dim Statement (Visual Basic) to declare a variable of a specific type. You can simultaneously specify its access level by using the Public (Visual Basic), Protected (Visual Basic), Friend (Visual Basic), or Private (Visual Basic) keyword, as in the following example.

Private x As Double
Protected s As String

The AscW and ChrW functions operate in Unicode. You should use them in preference to Asc and Chr, which must translate into and out of Unicode.