Program Example 15 String Handling 2

Transcription

1 Program Example 15 String Handling 2 Objectives Program Purpose Count the number of words, spaces and alphabetic characters in a sentence. Display the tally of letters Learning Goals To develop string handling techniques To use the functions MID, LEN and TRIM To use CHR and ASC functions Use of a variable array Use of parameter values Design Notes Arrays are used in Visual Basic for storing and processing large sets of similar values. Variable Arrays are arrays of variables used in memory for storing values. Arrays work very well with loops. This is because a loop can very quickly process all elements of an array using the index number. Arrays are declared in a similar fashion to normal variables, but their range must also be declared. For example, the code: Dim IntegerArray (13) as Integer declares an array of 14 integers. Dim Addresses(20) as String declares an array of 21 strings values (in this case, to store addresses). Interface Create the interface as shown below. Use 4 buttons, 1 text box, 1 list box and 8 labels.

2 Objects and Properties Type of Object Number Names of Objects Initial Properties of Objects Form 1 Form1 Text Text Processor 2 Text Box 1 txtinput Font Bold, 10 ListBox 1 lstletters Font Bold, 10 Labels 8 Label1, Label2, Label 3, Label4, Label5, lblchars, lblwords, lblspaces Command Buttons 4 btnexit, btnclear, btncountletters, btnloadpangram Font Bold, 12 Text as shown BorderStyle- Fixed3D where a value is to be displayed and changed Font Bold, 12: Text E&xit, C&lear, &Count Letters, &Load Pangram Further Initial Properties of Objects Object Property Initial Value Form1 Start Position Center Screen txtinput Text lstletters Multiline ColumnWidth MultiColumn True 50 True Label1 Caption Type in a Sentence Label2 Caption Number of Words Label3 Caption Number of Letters Label4 Caption Number of Spaces Label5 Caption Summary of Letters and Tally Code ** PUT THE FOLLOWING CODE IN THE GENERAL SECTION OF THE CODE WINDOW ** Dim count As Integer Dim charcount As Integer Dim spacecount As Integer counts words counts letters counts spaces Dim Letters(25) As Integer 'stores an array of 26 letters Const pangram1 = "Pack my box with five dozen liquor jugs" Const pangram2 = "Jackdaws love my big sphinx of quartz" Const pangram3 = "How quickly daft jumping zebras vex" '32 letters '31 letters '30 letters

3 Sub AddtoArray(ByVal LetterCode As Integer) 'only adds letters a-z and A-Z Select Case LetterCode Case 65 To 90 'Letter is uppercase - 65 to 90 LetterCode = LetterCode - 65 Letters(LetterCode) = Letters(LetterCode) + 1 Case 97 To 122 'Letter is lowercase - 97 to 122 LetterCode = LetterCode - 97 Letters(LetterCode) = Letters(LetterCode) + 1 Case End Select Sub DisplayArrayInListBox() Dim i As Integer lstletters.items.clear() For i = 0 To 25 lstletters.items.add(chr(i + 97) & " " & Letters(i) & " ") Next i Sub ClearArray() Dim i As Integer For i = 0 To 25 Letters(i) = 0 Next i Sub loadpangram() Dim randomnum As Integer Randomize() randomnum = Int(Rnd() * 3) + 1 Select Case randomnum Case 1 txtinput.text = pangram1 Case 2 txtinput.text = pangram2 Case 3 txtinput.text = pangram3 End Select ** COPY THE FOLLOWING CODE TO THE APPROPRIATE EVENTS ** Private Sub Form1_Load(ByVal ) Handles MyBase.Load loadpangram() Private Sub btnexit_click(byval sender ) Handles btnexit.click End

4 Private Sub btnclear_click(byval ) Handles btnclear.click txtinput.text = "" count = 0 spacecount = 0 lblnumwords.text = count lblnumletters.text = charcount lblnumspaces.text = spacecount ClearArray() DisplayArrayInListBox() Private Sub btncountletters_click(byval ) Handles btncountletters.click 'Actually it counts all characters except spaces Dim sentence As String Dim Letter As Integer Dim C As String to hold a single character ClearArray() spacecount = 0 sentence = txtinput.text.trim If sentence.length > 0 Then count = 1 For Letter = 1 To sentence.length C = sentence.substring(letter - 1, 1) AddtoArray(Asc(C)) 'only count characters in ASCII range and If (Asc(C) >= 65 And Asc(C) <= 90) Or (Asc(C) >= 97 And Asc(C) <= 122) Then charcount = charcount + 1 'add 1 to character count If C = " " Then spacecount = spacecount + 1 count = count + 1 Next Letter lblnumletters.text = charcount lblnumspaces.text = spacecount lblnumwords.text = count DisplayArrayInListBox() Private Sub txtinput_textchanged(byval ) Handles txtinput.textchanged btncountletters.performclick() Private Sub btnloadpangram_click(byval ) Handles btnloadpangram.click loadpangram()

5 Notes The table shows selected characters and their corresponding Ascii values. Character Ascii Value Character Ascii Value A 65 a 97 Z 90 z Space 32 Enter 13 Asc ( character ) will return the ASCII value of any character. Chr ( ascii value between 1 and 128 ) will change an ASCII value into a character. Suggestions for Consolidation and Extension 1. Modify the program by adding another list box called lstchars. It should work like the lstletters list box and display a tally of non-alphanumeric characters. You will need a new array declaration as well. 2. Create a program to display all ASCII characters and their corresponding values. Print it out and keep it for reference. Questions 1. What outputs do CHR(82) and CHR(43) return? 2. What outputs do ASC( K ) and ASC( k ) return? 3. What outputs do CHR(10) and CHR (13) return? 4. Consider the lines of code: If (Asc(C) >= 65 And Asc(C) <= 90) Or (Asc(C) >= 97 And Asc(C) <= 122) Then charcount = charcount + 1 'add 1 to character count If C = " " Then spacecount = spacecount + 1 count = count + 1 Can the code be simplified or written in a clearer fashion? 5. What other enhancements and modifications might be useful for these programs?