CIS162AD C

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CIS162AD - C

• Arrays part 112_arrays_loading.ppt

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Overview of Topics

• Declaring Arrays
• Loading Arrays
• Partially Filled Arrays
• Arrays Elements as Arguments
• Declaring and Loading Constant Arrays

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Arrays are Tables

• Array is a different word for a table.
• A table is made up of columns and rows.
• Just like an Excel spreadsheet.

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Array Defined

• An array is used to process a collection of data
  all of which is of the same data type (Integer,
  Decimal, String, etc.).
• First well look at single dimensional arrays
  (one column, many rows).
• Think of a single dimensional array as a list of
  variables.

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Declaring Array

• int intQty1, intQty2, intQty3int intQty
  new int3 //3 integer variablesdataType
  arrayName new dataTypearraySize
• An array of 3 elements of type integer is
  created.
• The arraySize is used by C to determine how much
  memory to allocate.
• Arrays will usually be class-level because after
  values are loaded in we dont want to lose the
  values.

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Array Subscript

• dataType arrayName new dataTypearraySize
  
• Arrays are allocated consecutive memory.
• Each element is referenced using a subscript.
• Subscript are integers.
• The number of elements that are created is
  arraySize.
• The first element in the array is referenced with
  a value of zero 0.
• The last element is referenced with a subscript
  value of arraySize 1.
• A subscript is also referred to as an index.
• Short variable names for subscripts are
  acceptable.

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Memory Map
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Subscript Out Of Range

• If during execution, the subscript value
  referenced an element past the end of the array,
  the program would throw an exception (run-time
  error).
• The programmer must make sure that the logic in
  the program does not allow the subscript to
  exceed the array size.
• This is called being out of range.

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Preventing Out of Range

• C will not prevent a subscript out of range
  error, but it will abort the execution when it
  happens.
• It aborts because the subscript would be
  referencing some other section of memory than
  what was allocated for the array.
• The programmer is responsible for preventing the
  out range error.
• We can use some built in methods to manage
  arrays, arrayName.Length arrayName.GetUpperBound
  (0).
• The For Each (foreach) command may also be used
  to walk through arrays.

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Array Properties

• int intQty new int3 //3 integer
  variables
• arrayName.Length
• intQty.Length is equal to 3.
• intQty.Length is the number of entries that can
  be loaded.
• The last valid subscript value is one less than
  Length.
• arrayName.GetUpperBound(0).
• intQty.GetUpperBound(0) is equal to 2.
• intQty.GetUpperBound(0) is last valid subscript
  value.
• Depending the loop structure, we may use
• less than Length or
• Equal to GetUpperBound(0)

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Array Processing

• Declare Array
• Load Array
• After creating the array, data must be loaded.
• Use arrayName.Length or arrayName.GetUpperBound(0)
  to prevent out of range errors.
• Note Arrays can be declared and loaded with
  constant values.
• Process Array
• Use individual elements in calculations or as
  arguments.
• Send entire arrays to methods for processing.
• Sort, Search, Display
• Use a lot of For loops or For Each loops.

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Declare Array

• //Arrays are declared at the class level,
• //so they can be referenced by all methods.int
  cintTestScores new int20int
  cintNumberOfStudents
• //We can load up to 20 scores, but we will
• //save how many tests are actually loaded in
  cintNumberOfStudents.

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Declare Array with a Const

• //Arrays can be declared using a constant for the
  size.const int intARRAY_SIZE 20int
  cintTestScores new intintArraySize//We can
  still load up to 20 scores

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cintTestScores Array Memory Map
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Load Array
cs12ex.txt 5040100301020

• //Loads Array with scores saved in a data file.
• private void btnLoadArray_Click( )
• FileStream studentFile new
  FileStream("cs12ex.txt", FileMode.Open)
• StreamReader studentStreamReader new
  StreamReader(studentFile) int i 0
  //subscript initialized to zero while
  (studentStreamReader.Peek() ! -1) if (i
  lt cintTestScores.Length)
  cintTestScoresi int.Parse(studentStreamReader.
  ReadLine( )) i //Increment
  subscript by one else
  MessageBox.Show (Array Size
  Exceeded) break //Get of out of loop
  Array is full. cintNumberOfStudents
  i //Save how many students were
  loadedstudentFile.Close( ) //Close
  file

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Loaded Arrays
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Process Array Individual Elements

• private void btnProcessArray_Click( )
• int iint intSum 0
• for (i 0 i lt cintTestScores.GetUpperBound(0)
  i)
• intSum cintTestScoresi
• txtSum.Text intSum.ToString(N0)

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For Each - Example

• private void btnProcessArray_Click( )
• int i //subscript not neededint intSum
  0
• foreach (int intTestScore in cintTestScores)
• intSum intTestScore
• txtSum.Text intSum.ToString(N0)

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Individual Elements as Arguments

• private void btnProcessArray_Click( )
• int idecimal decPercent
• for (i 0 i lt cintTestScores.GetUpperBound(0)
  i)
• decPercent calcPercent(cintTestScoresi)
• txtPercent.Text decPercent.ToString(N0)
• private decimal calcPercent(int intScore)
• return (intScore / 100)

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Partially Filled Arrays

• In the for loop on the prior slide it was assumed
  that the arrays were filled by going up to
  GetUpperBound(0).
• Up to 20 scores could be loaded, but in the
  example only 6 scores were actually loaded.
• When the array is not full, it is considered a
  partially filled array.
• The for loops need to be modified to only process
  the number scores loaded.
• The number of scores loaded are counted in the
  load routine, and the count should then be saved
  in a variable like cintNumberOfStudents.
• This variable should then be used when processing
  the arrays.

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Load Array Partially Filled

• //Loads Array with scores saved in a data file.
• private void btnLoadArray_Click( )
• FileStream studentFile new
  FileStream("cs12ex.txt", FileMode.Open)
• StreamReader studentStreamReader new
  StreamReader(studentFile) int i 0
  //subscript initialized to zero while
  (studentStreamReader.Peek() ! -1) if (i
  lt cintTestScores.Length)
  cintTestScoresi int.Parse(studentStreamReader.
  ReadLine( )) i //Increment
  subscript by one else
  MessageBox.Show (Array Size
  Exceeded) break //Get of out of loop
  Array is full. cintNumberOfStudents
  i //Save how many students were
  loadedstudentFile.Close( ) //Close
  file

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Processing Partially Filled Arrays

• private void btnProcessArray_Click( )
• int iint intSum
• //for (i 0 i lt cintTestScores.GetUpperBound(
  0) i) //process entire arrayfor (i 0 i
  lt mintNumberOfStudents i) //process partially
  filled array
• intSum cintTestScoresi
• txtAverage.Text (intSum / mintNumberOfStudents)
  .ToString(N0)

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Declare and Load Constant Arrays

• Arrays that will hold constants or some initial
  values can be loaded at declaration.
• When the values are provided at declaration, do
  not include the size. The size is determined by
  the number of values provided.
• The values are enclosed in braces and not
  parenthesis.decimal cdecPERCENT_RANGE new
  decimal 90D, 80D, 70D, 60D,
  0Dstring cstrLETTER_GRADE new string
  "A", "B", "C", "D", "F"
• C does NOT allow const for arrays.

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Summary

• Declaring Arrays
• Loading Arrays
• Partially Filled Arrays
• Arrays Elements as Arguments
• Declaring and Loading Constant Arrays