Microsoft Visual Basic 2010 Step by Step eBook

Chapter 13 Exploring Text Files and String Processing 329

String

Method or

Property

Visual

Basic

Function Description String Example

StartsWith N/A Determines whether

a string starts with a

specified string.

Dim str1 As String

Dim result As Boolean

str1 = "Hi Felix"

result = str1.StartsWith("Hi")

'result = True

EndsWith N/A Determines whether a string

ends with a specified string.

Dim str1 As String

Dim result As Boolean

str1 = "Hi Felix"

result = str1.EndsWith("Felix")

'result = True

Split Split Splits a string into substrings

based on a specified

separator and puts the

substring in an array.

Dim AllText As String = _

"a*b*c*1*2*3"

Dim strArray() As String

strArray = AllText.Split("*")

'strArray =

' {"a", "b", "c", "1", "2", "3"}

Sorting Text

An extremely useful skill to develop when working with textual elements is the ability to sort

a list of strings. The basic concepts in sorting are simple. You draw up a list of items to sort

and then compare the items one by one until the list is sorted in ascending or descending

alphabetical order.

In Visual Basic, you compare one item with another by using the same relational operators

that you use to compare numeric values. The tricky part (which sometimes provokes

long-winded discussions among computer scientists) is the specific sorting algorithm that

you use to compare elements in a list. We won’t get into the advantages and disadvantages

of different sorting algorithms in this chapter. (The bone of contention is usually speed,

which makes a difference only when several thousand items are sorted .) Instead, we’ll explore

how the basic string comparisons are made in a sort. Along the way, you’ll learn the skills

necessary to sort your own text boxes, list boxes, files, and databases.

Before Visual Basic can compare one character with another in a sort, it must convert each

character into a number by using a translation table called the ASCII character set (also

called the ANSI character set). (The acronym ASCII stands for American Standard Code for

Information Interchange .) Each of the basic symbols that you can display on your computer

has a different ASCII code. These codes include the basic set of “typewriter” characters

(codes 32 through 127) and special “control” characters, such as tab, line feed, and carriage

return (codes 0 through 31). For example, the lowercase letter a corresponds to the ASCII

code 97, and the uppercase letter A corresponds to the ASCII code 65. As a result, Visual Basic

treats these two characters quite differently when sorting or performing other comparisons.