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					Arrays
                   Objectives
• Declare and initialize a one-dimensional array
• Store data in a one-dimensional array
• Display the contents of a one-dimensional array
• Code a loop using the For Each…Next statement
• Access an element in a one-dimensional array
• Search a one-dimensional array
• Compute the average of a one-dimensional array’s
  contents
• Find the highest entry in a one-dimensional array
• Update the contents of a one-dimensional array
• Sort a one-dimensional array
          Objectives (cont’d)
• Create and manipulate parallel one-dimensional
  arrays
• Create a structure
• Declare a structure variable
• Create and manipulate a one-dimensional array
  of structures
• Create and initialize a two-dimensional array
• Store data in a two-dimensional array
• Search a two-dimensional array
                  Arrays
• A simple or scalar variable is one that is
  unrelated to any other variable in memory
• An array is a group of variables that have
  the same name and data type and are
  related in some way
         Arrays (continued)
• The most commonly used arrays are one-
  dimensional and two-dimensional
• Programmers use arrays to store related
  data in the internal memory of the
  computer
     One-Dimensional Arrays
• A one-dimensional array is simply a row
  (or column) of variables
• Each element in an array is identified by a
  subscript, which Visual Basic .NET
  assigns to the variable when the array is
  created
        One-Dimensional Arrays
             (continued)
• You refer to each variable in an array by
  its name and the variable’s subscript




Names of the variables in a one-dimensional array named
states
     One-Dimensional Arrays
          (continued)
• Declaring a one-dimensional array
  – Version 1
   {Dim | Private} arrayname(highestSubscript)
   As datatype
  – Version 2
   {Dim | Private} arrayname() As datatype =
   {initialValues}
     One-Dimensional Arrays
          (continued)
• Examples of declaring an array
  – Dim cities(3) As String
  – Private states() As String = {“Hawaii”,
    “Alaska”, “Maine”}
       Storing Data in a One-
         Dimensional Array
• In most cases, you use an assignment
  statement to enter data into an existing
  array
• Syntax: arrayname(subscript) = value
• Examples
  – cities(0) = “Madrid”
  – cities(1) = “Paris”
  – cities(2) = “Rome”
 Manipulating One-Dimensional
            Arrays
• You will learn how to perform the following
  tasks using a one-dimensional array:
  – Display the contents of an array
  – Access an array element using its subscript
  – Search the array
  – Calculate the average of the data stored in a
    numeric array
 Manipulating One-Dimensional
      Arrays (continued)
• You will learn how to perform the following
  tasks using a one-dimensional array
  (continued):
  – Find the highest value stored in an array
  – Update the array elements
  – Sort the array elements
  Displaying the Contents of a
    One-Dimensional Array
• uiDisplayButton’s Click event procedure
  – Demonstrates how you can display the
    contents of an array in a label control
  – Uses the For…Next statement to display each
    array element
  – You also could use the Do…Loop statement
    or the For Each…Next statement
    Displaying the Contents of a
      One-Dimensional Array
            (continued)




uiDisplayButton’s Click event procedure
The For Each…Next Statement




Syntax and an example of the For Each…Next statement
 Using the Subscript to Access
     an Element in a One-
      Dimensional Array
• XYZ Corporation pays its managers based
  on six different salary codes, 1 through 6
• Each code corresponds to a different
  salary
• uiSalaryButton’s Click event procedure
  displays the salary corresponding to the
  code entered by the user
 Searching a One-Dimensional
            Array
• The sales manager at Jacobsen Motors
  wants a procedure that allows him to
  determine the number of salespeople
  selling above a certain amount, which he
  will enter
• uiSearchButton’s Click event procedure
  searches the array, looking for values that
  are greater than the amount entered by
  the sales manager
Calculating the Average Amount
 Stored in a One-Dimensional
         Numeric Array
• uiCalcAvgButton’s Click event procedure
  calculates and displays the average test
  score




uiCalcAvgButton’s Click event procedure
Calculating the Average Amount
 Stored in a One-Dimensional
  Numeric Array (continued)




uiCalcAvgButton’s Click event procedure (continued)
 Determining the Highest Value
 Stored in a One-Dimensional
             Array
• Sharon Johnson wants a procedure that
  displays the highest amount she has
  earned in a week
• uiHighestButton’s Click event procedure
  will search the array, looking for the
  highest amount
Updating the Values Stored in a
   One-Dimensional Array
• The sales manager at Jillian Company
  wants a procedure that:
  – Allows her to increase the price of each item
    the company sells
  – Displays each item’s new price in the
    uiNewPricesLabel control

• uiUpdateButton’s Click event procedure
  performs these tasks
   Sorting the Data Stored in a
     One-Dimensional Array
• Arranging data in a specific order is called
  sorting
• Array.Sort method
  – Can be used to sort the elements in a one-
    dimensional array in ascending order
  – Syntax: Array.Sort(arrayname)
• uiSortButton’s Click event procedure uses
  the Array.Sort method to sort the numbers
  array in ascending order
   Sorting the Data Stored in a
     One-Dimensional Array
            (continued)
• To sort a one-dimensional array in
  descending order:
  – Use Array.Sort to sort the array in ascending
    order
  – Use Array.Reverse to reverse the array
    elements

• Syntax of the Array.Reverse method:
  Array.Reverse(arrayname)
   Using a Module-Level One-
       Dimensional Array
• Names application
  – Needs to display the names contained in a
    sequential access file
  – Should give the user the choice of displaying
    the names in either ascending or descending
    order

• The names array is declared in the form’s
  Declarations section, making it a module-
  level array
    Parallel One-Dimensional
              Arrays
• Arrays that are related by an element’s
  position (subscript)
• Searching one array gives you the
  subscript for the other array
• To store a price list, which includes a
  string and a number, you can use two one-
  dimensional arrays
  – A String array to store the product IDs
  – An Integer array to store the prices
       Parallel One-Dimensional
          Arrays (continued)




Illustration of a price list stored in two one-dimensional arrays
               Structures
• Structure statement: can be used to create
  your own data types in Visual Basic .NET
• Data types created using the Structure
  statement are referred to as user-defined
  data types or structures
• Members included in the structure can be
  variables, constants, or procedures
• In most cases, members are variables
         Structures (continued)




Syntax and an example of the Structure statement
  Using a Structure to Declare a
             Variable
• Variables declared using a structure are
  often referred to as structure variables




Syntax and an example of declaring a structure variable
   Using a Structure to Declare a
       Variable (continued)




Syntax and examples
of storing data in a
member variable
 Creating an Array of Structure
           Variables
• Assigning initial values to an array is
  referred to as populating the array
• Refer to a member variable in an array
  element using the syntax:
  arrayname(subscript).memberVariableNa
  me
     Two-Dimensional Arrays
• A two-dimensional array resembles a table
  in that the variables are in rows and
  columns




  Illustration of a two-dimensional array
     Two-Dimensional Arrays
          (continued)
• Each variable (element) in a two-
  dimensional array is identified by a unique
  combination of two subscripts
• The subscripts specify the variable’s row
  and column position in the array
• Refer to each variable in a two-
  dimensional array by the array’s name and
  the row and column subscripts
       Two-Dimensional Arrays
            (continued)




Syntax versions and examples of declaring a two-dimensional
array
            Storing Data in a Two-
              Dimensional Array




Syntax and examples of
entering data into a two-
dimensional array
  Searching a Two-Dimensional
             Array




uiDisplayPriceButton’s Click event procedure using a two-
dimensional array
    Searching a Two-Dimensional
         Array (continued)




uiDisplayPriceButton’s
Click event procedure
using a two-
dimensional array
(continued)
 The Tax Calculator Application
• John Blackfeather, the owner and
  manager of the Perrytown Gift Shop,
  should be able to use the application to
  calculate the weekly federal withholding
  tax for his employees
• To calculate the federal withholding tax,
  the user would need to enter the taxable
  wages in the Taxable wages text box and
  then click the Calculate Tax button
 The Tax Calculator Application
         (continued)




Interface for the Tax Calculator application
 The Tax Calculator Application
         (continued)




TOE chart for the Tax Calculator application
   Coding the uiCalculateButton
     Click Event Procedure




Pseudocode for the uiCalculateButton’s Click event procedure
   Coding the uiCalculateButton
     Click Event Procedure
           (continued)




Pseudocode for the uiCalculateButton’s Click event procedure
(continued)
                Summary
• Two versions of the syntax used to declare
  a one-dimensional array:
  – {Dim | Private} arrayname(highestSubscript)
    As datatype
  – {Dim | Private} arrayname() As datatype =
    {initialValues}
       Summary (continued)
• To refer to a variable in an array, use the
  array’s name followed by the variable’s
  subscript
• To create parallel one-dimensional arrays,
  create two one-dimensional arrays
• To create an array of structures, use the
  Structure statement to create a record
  structure, then use the record structure to
  declare the array
         Summary (continued)
• Two versions of the syntax used to declare a
  two-dimensional array:
  – {Dim | Private} arrayname(highestRowSubscript,
    highestColumnSubscript) As datatype
  – {Dim | Private} arrayname(,) As datatype =
    {{initialValues}, {initialValues},…{initialValues}}

• Syntax used to refer to a variable included in a
  two-dimensional array:
  arrayname(rowSubscript, columnSubscript)

				
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