6'1 Strings, Dates and Time

1
6.1 Strings, Dates and Time

• ASCII Processing Strings

2
Learning Objectives

• Explain how relational operators (lt gt) compare
  strings.
• Explain what the Instr, Mid and Len functions do.

3
ASCII

• American Standard Code for Information
  Interchange
• Upper case letters (A - Z) 65 - 90.
• Lower case letters (a z) 97 - 122.
• Numeric digits (0 9) 48 - 57.
• The space character is 32.

4
Processing Strings
5
Using relational operators

• gt or lt relates to alphabetical order.
• e.g. The following code will show 2 strings in a
  list box in alphabetical order.
• Dim Name1 As String
• Dim Name2 As String
• Name1 InputBox(Enter a name.)
• Name2 InputBox(Enter another name.)
• If Name1 lt Name2 Then
• lstAlphabetical.Items.Add(Name1)
• lstAlphabetical.Items.Add(Name2)
• Else
• lstAlphabetical.Items.Add(Name2)
• lstAlphabetical.Items.Add(Name1)
• End If

6
Searching for a substring using Instr

• The Instr function returns the position in the
  main string of the substring being searched for.
• e.g. The following code looks for man in the
  sentence The man looked up and saw the moon. It
  will then store its position as 5 in the variable
  Position.
• Assume declaration of variables below.
• MainString The man looked up and saw the
  moon.
• SearchString MAN
• Position Instr(MainString, SearchString)
• This is case insensitive unless you use a third
  parameter 1.

7
Processing individual characters using Mid

• The Mid function returns a substring from the
  main string.
• If given one number it will return the characters
  from that position to the end of the string.
• If given two numbers it will use the first as
  above and the second one to indicate how many
  characters to return.
• e.g. The following code will return the
  characters looking ahead. in the variable
  Characters and the character l in the variable
  Character.
• Dim Character As String
• Dim Characters As String
• MainString Keep on looking ahead.
• Characters Mid(MainString, 9)
• Character Mid(MainString, 9, 1)

8
Returning the length of a string

• Len returns the number of characters in a string.
• The following code will return 6.
• Dim EmployeeName As String
• Dim LengthOfString As Integer
• EmployeeName Mr Lee
• LengthOfString Len(EmployeeName)
• MsgBox(The length of the Employees name is
  LengthOfString)

9
Program 6.1 Validating a Full Name

• Specification
• Ask the user to enter a persons surname and then
  their first name into a single text box.
• Check that only one space character has been used
  between the names.

10
Program 6.1 Validating a Full Name

• Open a new project named Validating a Full
  Name.
• Set the text property of the form to Validating
  a Full Name.

11
Program 6.1 Validating a Full Name

• One label.
• One rich text box.
• Named rtfName.
• One button.
• Named butOK.

12
Program 6.1 Validating a Full Name

• butOK code
• Dim Spaces As Integer
• Dim EmployeeName As String
• Dim Index As Integer
• Dim Character As String
• EmployeeName rtfName.Text
• Len returns the length of the name. The loop is
  repeated this
• number of times to process each character in the
  name.
• For Index 1 To Len(EmployeeName)
• Character Mid(EmployeeName, Index, 1) Extract
  one character.
• If Character Then Is this character a
  space?
• Spaces Spaces 1 If yes, increment Spaces.
• End If
• Next Index
• If Spaces gt 1 Then Does the name have more than
  one space?
• MsgBox( Too many spaces!)
• End If

13
Program 6.1 Validating a Full Name

• Run the program and test it.
• Insert spaces in various different locations.

14
Extension

• Extend the program to output appropriate messages
  if one or more spaces are found
• Before the first name.
• After the surname.

15
Plenary

• How do relational operators (lt gt) compare
  strings?
• gt or lt relates to alphabetical order.
• What do the Instr, Mid and Len functions do?
• Instr returns the position in the main string of
  the substring being searched for.
• Mid returns a substring (from a specified
  location and of a specified length) from the main
  string.
• Len returns the number of characters in a string.

16
Homework

• Write a program that allows the user to
• Enter some text (this could be copied and pasted
  in).
• Enter a search letter.
• Outputs the number of times this letter occurs.
• Extension
• Adapt the program to count how many times a word
  is entered rather than a letter.