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

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

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 0 ... n-1, for array of size n

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

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

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

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];

Figure 9.3 Arrays onVacation, vacationDays, and dayOff

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 ([ ])

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

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

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

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 )

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

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

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

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;

Listing 9.4 Function sameArray

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);

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]; }

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

Listing 9.7 Function readScoresFile

Listing 9.7 Function readScoresFile (continued)

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

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

Listing 9.8 Function findIndexOfMin

Listing 9.8 Function findIndexOfMin (continued)

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

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.

Listing 9.9 The function linSearch

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

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

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

Listing 9.10 Function selSort

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