Programming Logic and Design Fourth Edition, Comprehensive Chapter 9 Advanced Array Manipulation.

Programming Logic and Design

Fourth Edition, Comprehensive

Chapter 9Advanced Array Manipulation

Programming Logic and Design, Fourth Edition, Comprehensive 2

Objectives

• Describe the need for sorting data

• Swap two values in computer memory

• Use a bubble sort

• Use an insertion sort

• Use a selection sort


Objectives (continued)

• Use indexed files

• Use a linked list

• Use multidimensional arrays


Understanding the Need for Sorting Records

• Sequential order: records are arranged based on the value in a field (e.g., SSN, employee ID)

• Random order: records are in the order in which they were added

• Sorting: placing the records in order, based on the values in one or more fields

• Ascending order: arranged from lowest to highest• Descending order: arranged from highest to lowest


Understanding the Need for Sorting Records (continued)

• Median value: the middle item when values are listed in order

• Mean value: arithmetic average

• Computer always sorts based on numeric values– Character data is sorted by its numeric code value– “A” is less than “B”– Whether “A” is greater than “a” is system-dependent


Understanding How to Swap Two Values

• Swapping two values: reversing their position• Use a temporary variable to hold one value


Using a Bubble Sort

• Bubble sort: – Items in a list are compared in pairs– If an item is out of order, it swaps places with the item

below it– In an ascending sort, after a complete pass through

the list, largest item has “sunk” to the bottom and smallest item has “bubbled” to the top


Using a Bubble Sort (continued)• Developing the application:

– Mainline logic



– housekeeping() module



– switchValues() module


Using a Bubble Sort (continued)

• Developing the application:– When to call switchValues() module



• Start with x = 0, compare first pair and swap

• With x = 1, compare next pair and swap


Using a Bubble Sort (continued)• With x = 2, compare next pair, but no swap needed

• With x = 3, compare last pair, and swap

• Largest value has “sunk” to the bottom



• Use nested loops for sorting an array

• Inner loop makes the pair comparisons

• Greatest number of comparisons is one less than the number of array elements

• Outer loop controls the number of times to process the list– One less than the number of array elements


Refining the Bubble Sort by Using a Constant for the Array Size

• Store the number of array elements in a constant

• Makes code more readable

• If number of elements changes later, only one change to the program is needed


Refining the Bubble Sort by Using a Constant for Array Size (continued)


Sorting a List of Variable Size

• Use a variable to hold the number of array elements• Declare the array with a large fixed size• Count the number of elements when the file is read

into the array• Use the count to control the loops when sorting,

ignoring unused slots in the array


Sorting a List of Variable Size (continued)


Refining the Bubble Sort by Reducing Unnecessary Comparisons

• After the first pass through the array:– Largest item must be at the end of array– Second largest item must be at the second-to-last

position in the array

• Not necessary to compare those two values again

• On each subsequent pass through the array, stop the pair comparisons one element sooner


Refining the Bubble Sort by Reducing Unnecessary Comparisons (continued)


Refining the Bubble Sort by Eliminating Unnecessary Passes

• Need one fewer pass than the number of elements to completely sort the array

• If array is somewhat ordered already, can reduce the number of passes

• Use a flag variable to indicate if there were any swaps during a single pass

• If no swaps, the array is completely sorted


Refining the Bubble Sort by Eliminating Unnecessary Passes (continued)


Using an Insertion Sort

• Bubble sort is one of the least efficient sorting methods

• Insertion sort usually requires fewer comparisons• Technique:

– Compare a pair of elements– If an element is smaller than the previous one, search

the array backward from that point and insert this element at the proper location


Using an Insertion Sort (continued)


Using a Selection Sort

• Selection sort: uses two variables to store the smallest value and its position in the array

• Technique:– Store first element value and its position in variables– Compare value of first element to value of next element– If next element is smaller, put its value and position in

the variables– Continue until end of array, at which time the smallest

value and its position are in the variables– Swap the first element value and position with the

element and position stored in the variables


Using a Selection Sort (continued)

• Technique (continued):– Start at the second element in the array and repeat the

process– Continue until all elements except the last have been

designated as the starting point– After making one less pass than the number of

elements, the array is sorted


Using a Selection Sort (continued)


Using Indexed Files

• When a large data file with thousands of records needs to be accessed in sorted order, usually only one field determines the sorting

• Key field: the field whose contents make the record unique

• Indexing records: create a list of key fields paired with their corresponding positions in the file

• Sorting the indexes is faster than physically sorting the actual records

• Random-access storage device: disk or other device from which records can be accessed in any order


Using Indexed Files (continued)

• Address: location within computer memory or storage

• Every data record on disk has an address

• Index: holds physical addresses and key field values

• Data file is in physical order, but index is sorted in logical order

• When a record is removed from an indexed file, does not have to be physically removed, just deleted from the index file


Using Linked Lists

• Linked list: requires one extra field in every record to hold the physical address of the next logical record


Using Linked Lists (continued)

• To add a new record:– Search the linked list for the correct logical location– Break the current link, and insert the new record by

linking the previous record to the new record and linking the new record to the next record


Using Linked Lists (continued)

• Two-way linked list: – Two fields are added to the data record– One holds address of previous logical record– One holds address of next logical record

• List can be accessed in either a forward or backward direction


Using Multidimensional Arrays

• Single-dimensional (or one-dimensional) array: represents a single list of values

• Multidimensional array: – A list with two or more related values in each position

• Two-dimensional array:– Represents values in a table or grid containing rows

and columns– Requires two subscripts


Using Multidimensional Arrays (continued)


Summary• Sort data records in ascending or descending order

based on the contents of one or more fields• Swap two values by creating a temporary variable to

hold one of the values• Bubble sort compares pairs and swaps pairs to obtain

the desired order• Eliminate unnecessary comparisons in each pass and

eliminate unnecessary passes to improve bubble sort• Insertion sort compares pairs, and moves the out-of-

place element to its proper place within the part of the array already processed


Summary (continued)

• Ascending selection sort uses two variables to hold the smallest value and its position in the array

• Index can be used to access records in logical order without physically sorting the data file

• Linked lists use an extra field to hold the address of the next record in the logical order

Programming Logic and Design Fourth Edition, Comprehensive Chapter 9 Advanced Array Manipulation.

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