1. Arrays … The Sequel Applications and Extensions
Chapter 10

2. Applying What You Learn
Searching through arrays efficiently
Sorting arrays
Using character arrays as "STRINGS"
strings … get it? hahahaha

3. Lists Defn => A collection of homogeneous components
linear collection
variable length collection
Length <=> the actual number of values stored in the list
Example -- a file of time card information
Joe, 40, Clyde, 38.5, Sniudly,

4. Lists Arrays can be used to implement a list
declare the array large
keep track of how many elements used
We often do operations on the lists
create a list, add an item, delete an item
print the list, search the list for a value
sort the list
A list of numbers
scores :

5. Sequential Search Consider the list unordered (not sorted)
For a function to search for a targert we must specify
name of the array to be searched
length of the list (number of array elements)
a flag parameter which tells whether or not the search was successful
an index value to be returned which tells where in the list the item was found
scores 5
boolean & found
int & location
scores :

6. Sequential Search Algorithm example
Note use of reference parameters for the found flag and the location
void search (int list[ ], int length, int target, boolean & found, int &location) { location = 0; while ((location < length) && (target != list[location])) location++; found = (index < length); } // if found == TRUE, location OK search (scores, 5, 92, found_it, where_its_at);
scores :

7. Sorted List -- Faster Search
Sorted list => components arranged in order
alphabetical
numerically ascending or descending
Advantage of a sorted list
need to search only until the value found is larger than target value

8. Sorting
Means arranging the list elements into some order (for instance, strings into alphabetical order, or numbers into ascending or descending order).
Dale Nell
Weems Chip
Headington Mark
Cooper Sonia
Huang Jeff
Cooper Sonia
Dale Nell
Headington Mark
Huang Jeff
Weems Chip
sorting

9. Sorting Algorithm
Make a pass through the list, look for smallest number
list 1 :
list 2 :

10. Sorting Algorithm
Make a pass through the list, look for smallest number
Write that number in another list, cross it off first list
list 1 :
list 2 : 57

11. Sorting Algorithm
Make a pass through the list, look for smallest number
Write that number in another list, cross it off first list
Repeat process, always look for smallest number remaining
list 1 :
list 2 :

12. Sorting Algorithm
Make a pass through the list, look for smallest number
Write that number in another column, cross it off first list
Repeat process, always look for smallest number remaining
Stop when all numbers have been crossed off

13. Sequential Search in a Sorted List
Note difference from previous search
void search_ord ( int list[ ], int target, int length, int & index, boolean & found)
{ index = 0; list [length] = target; // store an item beyond end while (target > list [index]) index++; found = (index < length && ltem = = list[index]; )
Explain how the last statement works

14. Inserting into an Ordered List
We wish to insert a new number into the list in the right position
find where it goes -- look until you find a number bigger than the new number 59
length : 5
list 2 :

15. Inserting into an Ordered List
We wish to insert a new number into the list in the right position
find where it goes -- look until you find a number bigger than the new number
shift that number all the rest of the elements down 59
length : 5
list 2 :
list 2 :

16. Inserting into an Ordered List
We wish to insert a new number into the list in the right position
find where it goes -- look until you find a number bigger than the new number
shift that number all the rest of the elements down
insert the new number in the vacated spot 59
length : 5
list 2 :
list 2 :

17. Inserting into an Ordered List
We wish to insert a new number into the list in the right position
find where it goes -- look until you find a number bigger than the new number
shift that number all the rest of the elements down
insert the new number in the vacated spot
be sure to increment the length
length : 5
length : 6
list 2 :

18. Binary Search in an Ordered List
Examines the element in the middle of the array.
Is it the sought item?
If so, stop searching.
Is the middle element too small?
Then start looking in second half of array.
Is the middle element too large?
Then begin looking in first half of the array.
Repeat the process in the half of the list that should be examined next.
Stop when
item is found, or when
there is nowhere else to look and it has not been located.

19. String Library Routines
String assignment
String comparison: returns -1 if s1 < s2 returns 0 if they are equal returns +1 if s1 > s2
Returns length of the string

20. Using typedef with Arrays
Specify an array type
this can be used throughout program
helps program self document
Example :
typedef char default_string [80];
defalt_string fname, descrip; void reverse (default_string s);

21. Two dimensional Arrays
A collection of components
all of the same type
structured in TWO dimensions
each component accessed by a PAIR of indices representing the component’s position in each dimension 1 2 3
Which cell is Location (2,3) ?

22. Declaring Two Dimensional Arrays
Syntax: data_type array_name [row_dim][col_dim];
Example:
First element is int_table[0][0]
Last element is int_table[4][3]
int int_table [5][4]; 1 2 3

23. Processing Two-D Arrays
Arrays processed in some pattern
random
along rows
along columns
whole array
We will use the declaration shown below:
int int_table [5][4]; int row, col;

24. Processing Two-D Arrays
What does the routine below do with the array? What should we name the function?
total_a_row

25. Processing Two-D Arrays
What does this routine below do with the array? What should we name the function?
total_column

26. Processing Two-D Arrays
This function initializes an array.
Fill in the blanks with the correct identifiers 3
col
table
value

27. Printing a Table We must process each row, item by item
Which will be the inner loop? Which will be the outer loop?
The LCV of the inner loop must be the one which changes the most often
row
What goes here?
col
endl

28. Passing Arrays as Parameters
Recall declaration for 1-D array
we didn’t specify the size in the brackets
we sent the size as a separate parameter
Recall name of the array is a pointer constant
tells where the array starts in memory
this is what is passed to the function
void whatever ( float num_list [ ], int size);

29. Passing 2-D Arrays as Parameters
For a 2-D array, declare
We are sending the starting address
also how many elements it takes to jump us to the next row
that is -- the number of columns
Note that this could be for an array for ANY number of rows, but exactly 4 columns
As with 1-D, we also send another parameter for the function as a limiting value
void whatever ( float num_table [ ][4], int num_rows);

30. Alternate 2-D Array Definition
Think of the 2-D array as an array of arrays
Example
Each element of renters is an array of rent_pmts
typedef float rent_pmts [12]; rent_pmts renters [6]; … 1 … 5

31. Multidimensional Arrays
C++ arrays not limited to two dimensions
limitation is amount of memory
const int NUM_BLDGS = 10; const int APTS_PER_BLDG = 12; float apt_pmts [NUM_BLDGS][6][APTS_PER_BLDG];

32. Multidimensional Arrays
C++ arrays not limited to two dimensions
limitation is amount of memory
const int NUM_BLDGS = 10; const int APTS_PER_BLDG = 12; float apt_pmts [NUM_BLDGS][6][APTS_PER_BLDG];
This gives a 3-D array with 720 items apt_pmt [bldg][tennant][apt]

33. Testing and Debugging Initialize all components of an array
no guarantee of what is there to start with
Use the same number of indeces as the declaration of array
Make sure indeces are in order
don’t reverse row and column references

34. Testing and Debugging
Use meaningful identifiers for the array name and indeces
Double check upper and lower bounds on indeces
don’t walk off the edge of the array
When declaring multidimensional array as a formal parameter
must state sizes of all but first dimension

35. Testing and Debugging When calling function with array as parameter
sizes of multi-dim actual parameter must match exactly sizes of formal
Use typedef statement to define multi-dimensional array type
use this for actual and formal parameter declaration