Case, Arrays, and Structures

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Case, Arrays, and Structures
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Summary Slide

• Case Structure
• Select Case - Numeric Value Example 1
• Select Case - String Value Example
• Arrays
• Declaring and Allocating Arrays
• Array Declaration Example
• Passing Arrays to Procedures
• Example Passing Arrays
• Multidimensional Rectangular and Jagged Arrays
• For Each/Next Repetition Structure
• Example Multidimensional Array with Each/Next
  Repetition
• Structures
• Example of a Structure
• Structures and Classes
• Structure Variables
• Structures and Arrays

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Case Structure

• Best alternative for testing a single variable or
  expression for multiple values
• Any decisions coded with nested If statements can
  also be coded using Case structure
• Case Structure is simpler, cleaner, more
  efficient than the nested If

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Select Case General Form(also notice indenting)

• Select Case expression
• Case ConstantList
• code to run
• Case ConstantList
• code to run
• Case Else
• code to run
• End Select

If expressionvalue in constant list
If expressionvalue in constant list
If expressionlt gtvalues in any of the preceding
constant lists
Case Else is an optional clause
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Select Case - Numeric Value Example 1

• Select Case intScore
• Case Is gt 100
• lblMsg.Text"Excellent Score"
• Case 80 to 99
• lblMsg.Text"Very Good"
• Case 60 to 79
• lblMsg.TextAverage Score"
• Case Else
• lblMsg.Text"Improvement Needed"
• End Select

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Select Case - String Value Example

• Select Case txtTeam.Text.ToUpper( )
• Case "TIGERS"
• (Code for Tigers)
• Case "LEOPARDS"
• (Code for Leopards)
• Case "COUGARS", "PANTHERS"
• (Code for Cougars and Panthers)
• End Select

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About Arrays

• Arrays are data structures consisting of data
  items of the same type
• Position number
• Values that indicate specific locations within
  arrays
• The first element in every array is the zero
  element
• Length property
• Every array in Visual Basic knows its own
  length through the Length property
• GetUpperBound method
• Returns the index of the last element in the
  array
• The value returned by this GetUpperBound is one
  less than the value of the arrays Length property

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Arrays
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Declaring and Allocating Arrays

• Generally speaking, there are two ways to declare
  arrays
• Intitializer lists (if you know the values of the
  array during coding)
• Declare and populate method (if you do not know
  the values of the array elements during coding
  because they will be dynamically loaded to the
  array)
• The amount of memory required by an array
  depends on the length of the array and the size
  of the data type of the elements in the array

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Array Declaration Example
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Passing Arrays to Procedures

• Passing the Array
• Specify the name of the array without using
  parentheses
• Every array object knows its own upper bound
• Do not need to pass the upper bound of the array
  as a separate argument
• In Visual Basic, arrays always are passed by
  reference
• Receiving the array
• The procedures parameter list must specify that
  an array will be received

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Example Passing Arrays
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Multidimensional Rectangular and Jagged Arrays

• Multidimensional arrays (multiple-subscripted)
• Require two or more indices to identify
  particular elements
• Rectangular arrays
• Two indices, first identifies the elements row,
  the second the elements column
• A rectangular two-dimensional array with m rows
  and n columns is called an m-by-n array
• Jagged arrays
• Jagged arrays are maintained as arrays of arrays
• Rows in jagged arrays can be of different lengths

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For Each/Next Repetition Structure

• For Each/Next
• Provided to iterate through the values in a data
  structure, such as an array
• Instead of a counter, For Each/Next uses a
  variable to represent the value of each element
• Useful when the indices of the elements are not
  important
• Particularly useful for looping through arrays of
  objects

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Example Multidimensional Array with Each/Next
Repetition
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Structures

• A structure is a combination of multiple fields
  of related data.
• The Structure declaration cannot go inside a
  procedure
• Structure statements are typically placed at the
  top with the module level declarations or in a
  separate class
• Once you have created a structure, you can
  declare variables of the structure, just as if it
  were another data type

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Example of a Structure
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Structures and Classes

• Structures and classes are similar in the
  following respects
• Both have members, including constructors,
  methods, properties, fields, constants,
  enumerations, and events.
• Both can implement interfaces.
• Both can have shared constructors, with or
  without parameters.
• Structures and classes differ in the following
  particulars
• Structures are value types classes are reference
  types.
• All structure members are Public by default
  class variables and constants are Private by
  default
• Structure variable declarations cannot specify
  initializers, the New keyword, or initial sizes
  for arrays class variable declarations can.
• Structures implicitly inherit from the ValueType
  class and cannot inherit from any other type
  classes can inherit from any class or classes
  other than ValueType.
• Structures are not inheritable classes are.
• Structures are never terminated, so the common
  language runtime (CLR) never calls the Finalize
  method on any structure

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Structure Variables

• Once you have created a structure, you can
  declare procedure-level and module-level
  variables as that type. For example, you can
  create a structure that records information about
  a computer system, as in the following code
• You can now declare variables of that type, as
  follows
• To assign and retrieve values from the elements
  of a structure variable, you use the same syntax
  as you use to set and get properties on an
  object.

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Structures and Arrays

• A structure can contain an array as one of its
  elements
• You access the values of an array within a
  structure the same way you access a property on
  an object
• You can also declare an array of structures