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

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
Programming Logic and Design, Fourth Edition, Comprehensive

3. Objectives (continued)
Use indexed files
Use a linked list
Use multidimensional arrays
Programming Logic and Design, Fourth Edition, Comprehensive

4. 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
Programming Logic and Design, Fourth Edition, Comprehensive

5. 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
Programming Logic and Design, Fourth Edition, Comprehensive

6. Understanding How to Swap Two Values
Swapping two values: reversing their position
Use a temporary variable to hold one value
Programming Logic and Design, Fourth Edition, Comprehensive

7. 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
Programming Logic and Design, Fourth Edition, Comprehensive

8. Using a Bubble Sort (continued)
Developing the application:
Mainline logic
Programming Logic and Design, Fourth Edition, Comprehensive

9. Using a Bubble Sort (continued)
Developing the application:
housekeeping() module
Programming Logic and Design, Fourth Edition, Comprehensive

10. Using a Bubble Sort (continued)
Developing the application:
switchValues() module
Programming Logic and Design, Fourth Edition, Comprehensive

11. Using a Bubble Sort (continued)
Developing the application:
When to call switchValues() module
Programming Logic and Design, Fourth Edition, Comprehensive

12. Using a Bubble Sort (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

13. Using a Bubble Sort (continued)
Start with x = 0, compare first pair and swap
With x = 1, compare next pair and swap
Programming Logic and Design, Fourth Edition, Comprehensive

14. 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
Programming Logic and Design, Fourth Edition, Comprehensive

15. Using a Bubble Sort (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

16. Using a Bubble Sort (continued)
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
Programming Logic and Design, Fourth Edition, Comprehensive

17. 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
Programming Logic and Design, Fourth Edition, Comprehensive

18. Refining the Bubble Sort by Using a Constant for Array Size (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

19. Refining the Bubble Sort by Using a Constant for Array Size (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

20. 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
Programming Logic and Design, Fourth Edition, Comprehensive

21. Sorting a List of Variable Size (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

22. Sorting a List of Variable Size (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

23. 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
Programming Logic and Design, Fourth Edition, Comprehensive

24. Refining the Bubble Sort by Reducing Unnecessary Comparisons (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

25. 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
Programming Logic and Design, Fourth Edition, Comprehensive

26. Refining the Bubble Sort by Eliminating Unnecessary Passes (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

27. 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
Programming Logic and Design, Fourth Edition, Comprehensive

28. Using an Insertion Sort (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

29. Using an Insertion Sort (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

30. 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
Programming Logic and Design, Fourth Edition, Comprehensive

31. 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
Programming Logic and Design, Fourth Edition, Comprehensive

32. Using a Selection Sort (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

33. 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
Programming Logic and Design, Fourth Edition, Comprehensive

34. 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
Programming Logic and Design, Fourth Edition, Comprehensive

35. Using Linked Lists
Linked list: requires one extra field in every record to hold the physical address of the next logical record
Programming Logic and Design, Fourth Edition, Comprehensive

36. 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
Programming Logic and Design, Fourth Edition, Comprehensive

37. 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
Programming Logic and Design, Fourth Edition, Comprehensive

38. 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
Programming Logic and Design, Fourth Edition, Comprehensive

39. Using Multidimensional Arrays (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

40. Using Multidimensional Arrays (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

41. 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
Programming Logic and Design, Fourth Edition, Comprehensive

42. 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