1. Chapter 9: Data Structures: Arrays
Problem Solving,
Abstraction, and Design using C++ 6e
by Frank L. Friedman and Elliot B. Koffman

2. 9.1 The Array Data Type Array elements have a common name
The array as a whole is referenced through the common name
Array elements are of the same type — the base type
Individual elements of the array are referenced by sub-scripting the group name
element’s relative position used, beginning with 0
Array stored in consecutive memory locations

3. Additional Array Details
Subscripts are denoted as expressions within brackets: [ ]
Base type can be any fundamental, library-defined, or programmer -defined type
The index type is integer and the index range must be n-1, for array of size n

4. element-type array-name [array-size];
Array Declaration
element-type array-name [array-size];
Type of all the values in the array
Name of the entire collection of values
Integer expression indicating number of elements in the array

5. Example 1
element-type array-name [array-size] = {initialization-list};
float x[8] = {16.0, 12.0, 6.0, 8.0, 2.5, 12.0, 14.0, -54.5};
16.0
12.0
6.0
8.0
2.5
14.0
-54.5

6. Example 1 (con’t) cout << x[0]; x[3] = 25.0; sum = x[0] + x[1];
x[2] = x[0] + x[1];

7. Example 2 const int NUM_EMP = 10; bool onVacation[NUM_EMP];
int vacationDays[NUM_EMP];
enum day {sunday, monday, tuesday, wednesday, thursday, friday, saturday};
day dayOff[NUM_EMP];
float plantHours[7];

8. Figure 9.3 Arrays onVacation, vacationDays, and dayOff

9. Array Initialization
List of initial values enclosed in braces ({ }) following assignment operator (=)
Values from initialization list are assigned in order to array elements
Length of initialization list cannot exceed size of the array
If too few values, value assigned is system dependent
Size of array can be automatically set to number of initializing values using empty brackets ([ ])

10. Array Subscripts Enclosed in brackets ([ ])
Indicates which element is referenced by position
Array subscript value is different than array element value
Subscript can be an expression of any integral type
To be valid, subscript must be a value between 0 and one less than the array size

11. 9.2 Sequential Access to Array Elements
Random Access
Access elements is any order
Sequential Access
Process elements in sequential order starting with the first

12. Example of Sequential Access
int cube[10];
for (int i = 0; i < 10; i++)
cube[i] = i * i * i;

13. Strings and Arrays of Characters
string object uses an array of char
Can reference individual character of a string object in different ways
name[ i ]
name.at( i )
Other member functions of string class
message.length( i )

14. 9.3 Array Arguments
Use <, ==, >, +, -, etc. to test and modify array elements individually
Can pass array elements to functions
exchange (s[3], s[5]);

15. Listing 9.3 Function to exchange the contents of two floating-point memory locations

16. Passing an Array Argument
Arrays are always passed by reference
Pass entire array to a function by writing just its name (no subscripts or brackets) in the argument list of the function call
In function definition and prototype, user empty brackets ([ ]) to identify array
Use keyword const to indicate that array argument cannot be changed by function

17. Example 1 const int MAX_SIZE = 5; float x[MAX_SIZE ];
float y[MAX_SIZE ];
. . .
if (sameArray(x, y, MAX_SIZE))
cout << “Arrays are identical.” << endl;
else
cout << “Arrays are different.” << endl;

18. Listing 9.4 Function sameArray

19. Example 2 const int MAX_SIZE = 5;
float x[MAX_SIZE ] = {1.8, 2.2, 3.4, 5.1, 6.7};
float y[MAX_SIZE ] = {2.0, 4.5, 1.3, 4.0, 5.5};
float z[MAX_SIZE];
. . .
addArray(MAX_SIZE, x, y, z);

20. Listing 9.5 Function addArray
// File: addArray.cpp
// Stores the sum of a[i] and b[i] in c[i]
// Sums pairs of array elements with subscripts ranging from 0
// to size – 1
// Pre: a[i] and b[i] are defined (0 <= i <= size-1)
// Post: c[i] = a[i] + b[i] (0 <= i <= size-1)
void addArray
(int size, // IN: the size of the arrays
const float a[], // IN: the first array
const float b[], // IN: the second array
float c[]) // OUT: result array {
// Add corresponding elements of a and b and store in c
for (int i = 0; i < size; i++)
c[i] = a[i] + c[i]; }

21. 9.4 Reading Part of an Array
Sometimes it is difficult to know how many elements will be in an array
150 students in one section
200 students in another section
Always allocate enough space for largest possible amount needed
Remember to start reading with index [0]
Must keep track of how many elements used

22. Listing 9.7 Function readScoresFile

23. Listing 9.7 Function readScoresFile (continued)

24. 9.5 Searching and Sorting Arrays
Two common array processing problems
Searching
Sorting
E.g.
look for a particular score, highest score, etc.
rearrange an array of scores in increasing order

25. Finding the Smallest Value
1. Assume the first element is smallest so far and save its subscript
2. For each array element after the first one
2.1 If the current element < the smallest so far
2.1.1 Save the subscript of current element

26. Listing 9.8 Function findIndexOfMin

27. Listing 9.8 Function findIndexOfMin (continued)

28. Array Search - Interface
Input arguments
int items[ ] // array to search
int size // number of items in array
int target // item to find
Output arguments
none
Returns
if found, subscript of first location in array
if not found, -1

29. Array Search - Algorithm
1. For each array element
1.1 If the current element contains the target
1.2 Return the subscript of the current element
2. Return -1.

30. Listing 9.9 The function linSearch

31. Sorting an Array in Ascending Order
Many programs execute more efficiently if data is in order before processing starts
Possible to order in either ascending or descending arrangement
Selection sort just one of many ways to do this
reuses previous components of search and swap operations

32. Selection Sort Input arguments Output arguments Local variables
float items[ ] // array to sort
int n // number of items to sort
Output arguments
int items [ ] // original array sorted
Local variables
int i // subscript of first element
int minSub // subscript of smallest item

33. Selection Sort - Algorithm
1. Starting with the first item in the array (subscript 0) and ending with the next-to-last-item:
1.1 Set i equal to the subscript of the first item in the subarray to be processed in the next steps
1.2 Find the subscript (minSub) of the smallest item in the subarray with subscripts ranging from i through n-1
1.3 Exchange the smallest item found in step 1.2 with item i

34. Listing 9.10 Function selSort

35. 9.13 Common Programming Errors
Arrays
Out-of-range subscript references
Unsubscripted array references
Subscripted references to nonarray variables
Mixing types in passing arrays to functions