Arrays provide the programmer with a way of organizing a collection of homogeneous data items into a single data structure.

1
Arrays

• Arrays provide the programmer with a way of
  organizing a collection of homogeneous data items
  into a single data structure.
• An array is a data structure that is made up of a
  number of variables all of which have the same
  data type and name.
• The individual data items that make up the array
  are referred to as the elements of the array.
• Elements in the array are distinguished from one
  another by the use of an index or subscript,
  enclosed in parentheses, following the array name
  e.g., scores (3)

2
Operations on Arrays

• The most typical operations performed on arrays
  are
• Loading a set of initial values into the elements
  of an array
• Processing the elements of an array
• Searching an array, using a linear or binary
  search, for a particular element
• Writing out the contents of an array to a report
• Usually, the elements of an array are processed
  in sequence, from first to last.

3
Writing Algorithms that Manipulate Arrays

• Array algorithms are written using a DO or
  DOWHILE loop.
• In each algorithm, the contents of the array and
  the number of elements have been established and
  the subscript is named index.
• The number of elements in the array is stored in
  the variable numElements.

4
Initializing an Array

• One common procedure is to read a fixed number of
  input values into the elements of an array from
  an input file.
• Another procedure loads a variable number of
  values into an array. It must include a sentinel
  and a check to ensure that no attempt is made to
  load more entries into the array than the array
  can hold.

5

• Initialize Fixed Array
• Read numElements
• DO index 1 TO numElements
• READ inputValue
• SET array(index) inputValue
• ENDDO
• END

6
A Linear Search of an Array

• A linear search involves looking at each of the
  elements of the array, one by one, starting with
  the first element.
• Continue the search until either you find the
  element being looked for or you reach the end of
  the array.
• A linear search is often used to validate data
  items.
• The pseudocode algorithm for a linear search of
  an array will require a boolean flag named
  elementFound. (See next slide for example.)

7
Example Calculate Freight Charge

• Design an algorithm that will read an input
  weight for an item to be shipped, search an array
  of shipping weights, and retrieve a corresponding
  freight charge.
• An array, shipping_weights, contains a range of
  shipping weights in ounces, and an array,
  freight_charges, contains a corresponding array
  of freight charges in dollars

Shipping Weight
Freight Charge
3.00
5.00
7.50
12.00
16.00
35.00
100 oz.
500 oz.
1000 oz.
3000 oz.
5000 oz.
9999 oz.
8

• Calculate Freight Charges
• Set numElements 6
• SET index 1
• SET elementFound false
• PROMPT entryWeight
• GET entryWeight
• DOWHILE (NOT elementFound AND index lt
  numElements)
• IF (shipping(index) lt entryWeight) THEN
• SET index index 1
• ELSE
• SET elementFound true
• ENDIF
• ENDDO
• IF (elementFound) THEN
• charge freight(index)
• DISPLAY charge
• ELSE
• DISPLAY Invalid Weight
• ENDIF