UTPA – Fall 2011

1. CSCI 3327 Visual Basic Chapter 12: Strings, Characters and Regular Expressions UTPA – Fall 2011

2. Objectives • In this chapter, you will • Learn how to create and manipulate String objects • Get familiar with common methods of String class • Learn how to create and manipulate StringBuilder objects • Know how to use regular expressions in conjunction with classes Regex and Match • Learn how to search for patterns in text using regular expressions

3. Online Chapters • URL: • www.pearsonhighered.com/deitel/ • Chapter 17 - Download: PDF

4. String Class vs. StringBuilder Class • String’s contents can never change • Operations that seem to concatenate Strings are in fact creating new Strings • StringBuilder class is different

5. StringBuilder Class • Imports System.Text • Constructor • Dim buffer1 AsNew StringBuilder() • Dim buffer2 AsNew StringBuilder(10) • Dim buffer3 AsNew StringBuilder(“hello”) • Initial capacity is the smallest power of two greater than or equal to the number of characters in the argument with a minimum of 16

6. Example 17.9: StringBuilderConstructor.vb • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

7. Length and Capacity Properties • Length property • The number of characters in a StringBuilder object • Capacity property • The number of characters that a StringBuilder object can store without allocating more memory

8. Example 17.10: StringBuilderFeatures.vb • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html • Function EnsureCapacity(75) • Truncate StringBuilder length • buffer.Length = 10

9. Append Method • Each method has versions for primitive type and for character arrays, Strings and Objects • buffer.Append(“hello”) • buffer.Append(objectValue) • buffer.Append(characterArray) • buffer.Append(characterArray, 0, 3) • Example 17.11: StringBuilderAppend.vb • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

10. Example 17.12: AppendFormat Method • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html • string1 = “this {0} costs: {1:C}.” • buffer.AppendFormat(string1, objectArray) • {X[, Y][:FormatString]} • The number of the argument to be formatted (starting from zero) • Y is an optional argument • The String will be padded with spaces • {0:D3} – three-digit decimal • {0, 4}, {0, -4}

11. Insert and Remove Methods • Insert • Primitive types • Character arrays, Strings and Objects • Remove(arg1, arg2) • arg1 – the index at which to begin deletion • arg2 – the number of characters to delete

12. Example 17.13: StringBuilderInsertRemove.vb • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

13. Example 17.14: Replace Method • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html • builder.Replace(string1, string2) • builder.Replace(“g”c, “G”c, index, count)

14. Char Methods • Methods of structure Char • Char.IsDigit(character) • Char.IsLetter(character) • Char.IsLower(character) • Char.IsUpper(character) • Char.IsPunctuation(character) • Char.IsWhiteSpace(character)

15. Example 17.15: SharedCharMethodsForm.vb • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

16. Regular Expression • Formatted strings • E.g. zip code – five digits • Imports System.Text.RegularExpressions • Regex object • Dim expression As New Regex(“e”) • expression.Match(testString) • expression.Matches(testString)

17. Example 17.16: BasicRegex.vb • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html • ForEach myMatch In expression.Matches(testString) • Quantifier • Dim expression As New Regex(“regexp?”) • Alternation • Dim expression As New Regex(“(c|h)at”)

18. Character Classes • \d • Any digit • \w • Any word character • \s • Any whitespace • \D • Any nondigit • \W • Any nonword character • \S • Any nonwhitespace

19. Example 17.18: CharacterClasses.vb • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html • \w+ • \w+? • [a-f] • [^a-f] • [a-zA-Z]+ • .*

20. Other Quantifiers in Regular Expressions

21. Example 17.20: Validate.vb • URL: • http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html • [\d-[4]] • Any digits other than 4