Arrays Chapter 8 Arrays Hold Multiple Values n

Arrays Chapter 8

Arrays Hold Multiple Values n n n Array: variable that can store multiple values of the same type Values are stored in adjacent memory locations Declared using [] operator int tests[5];

Array Storage in Memory n The definition int tests[5]; allocates the following memory first second third fourth fifth element element

Array Terminology In the definition int tests[5]; n int is the data type of the array elements n n n tests is the name of the array 5, in [5], is the size declarator. It shows the number of elements in the array. The size of an array is the number of bytes allocated for it (number of elements) * (bytes needed for each element)

Array Terminology Examples n Examples: Assumes int uses 4 bytes and double uses 8 bytes int tests[5]; // holds 5 ints; // size is 20 bytes double volumes[10]; // holds 10 doubles // size is 80 bytes

Accessing Array Elements n n Each array element has a subscript, used to access the element. Subscripts start at 0 subscripts 1 2 3 4 5

Accessing Array Elements n Array elements (accessed by array name and subscript) can be used as regular variables tests 1 2 3 4 5 tests[0] = 79; cout << tests[0]; cin >> tests[1]; tests[4] = tests[0] + tests[1]; cout << tests; // illegal due to // missing subscript

Array Subscripts n n Array subscript can be an integer constant, integer variable, or integer expression Examples: Subscript is cin >> tests[3]; int constant cout << tests[i]; int variable cout << tests[i+j]; int expression

Global vs. Local Arrays n n Global arrays initialize all elements n Numeric elements are initialized to 0 n Strings and characters are initialized to NULL Local arrays leave all elements uninitialized by default n It is the programmer’s job to make sure they are initialized before they are used

Inputting and Displaying Array Contents n To access a single element of an array, use a subscript (as previously shown) int tests[5]; // Define 5 -element array cout << “Enter first test score ”; cin >> tests[0];

Inputting and Displaying All Array Elements n To access each element of an array n n n Use a loop Let the loop control variable be the array subscript A different array element will be referenced each time through the loop for (i = 0; i < 5; i++) cout << tests[i] << endl;

Getting Array Data from a File int sales[5]; ifstream datafile; datafile. open("sales. dat"); if (!datafile) cout << "Error opening data filen"; else { // Input daily sales for (int day = 0; day < 5; day++) datafile >> sales[day]; datafile. close(); }

No Bounds Checking n n n There are no checks in C++ that an array subscript is in range An invalid array subscript can cause program to overwrite other memory Example: num int i = 4; int num[3]; num[i] = 25; 25 [0] [1] [2]

Array Initialization n Can be initialized during program execution with assignment statements tests[0] = 79; tests[1] = 82; // etc. n Can be initialized at array definition with an initialization list int tests[5] = {79, 82, 91, 77, 84};

Partial Array Initialization n If array is initialized at definition with fewer values than the size declarator of the array, remaining elements will be set to 0 or NULL int tests[5] = {79, 82}; 79 n 82 0 0 0 Initial values used in order; cannot skip over elements to initialize noncontiguous range

Implicit Array Sizing n Can determine array size by the size of the initialization list short quizzes[]={12, 17, 15, 11}; 12 n 17 15 11 Must use either array size declarator or initialization list when array is defined

Processing Array Contents n Array elements can be n n n treated as ordinary variables of the same type as the array used in arithmetic operations, in relational expressions, etc. Example: if (principal. Amt[3] >= 10000) interest = principal. Amt[3] * int. Rate 1; else interest = principal. Amt[3] * int. Rate 2;

Using Increment and Decrement Operators with Array Elements n When using ++ and -- operators, don’t confuse the element with the subscript tests[i]++; tests[i++]; // adds 1 to tests[i] // increments i; but has // no effect on tests

Sum of Array Elements n Use a simple loop to add together array elements float average, sum = 0; for (int tnum = 0; tnum < 5; tnum++) sum += tests[tnum]; n Once summed, average can be computed average = sum/5;

Largest Array Element n Use a loop to examine each element and find the largest element (i. e. , one with the largest value) int largest = tests[0]; for (int tnum = 1; tnum < 5; tnum++) { if (tests[tnum] > largest) largest = tests[tnum]; } cout << “Highest score is ” << largest; n A similar algorithm exists to find the smallest element

C-Strings and string Objects n Can be processed using array name n n Entire string at once or One element at a time (by using a subscript) string city; cout << "Enter city name: "; cin >> city; 'S' city[0] 'a' 'l' 'e' 'm' city[1] city[2] city[3] city[4]

Using Parallel Arrays n n Parallel arrays: two or more arrays that contain related data Subscript is used to relate arrays n n elements at same subscript are related The arrays do not have to hold data of the same type

Parallel Array Example int size = 5; string name[size]; // student name float average[size]; // course average char grade[size]; // course grade name 0 1 2 3 4 average 0 1 2 3 4 grade 0 1 2 3 4

Parallel Array Processing int size = 5; string name[size]; // student name float average[size]; // course average char grade[size]; // course grade. . . for (int i = 0; i < size; i++) cout << " Student: " << name[i] << " Average: " << average[i] << " Grade: " << grade[i] << endl;

The typedef Statement n n Creates an alias for a simple or structured data type Format: typedef existing. Type new. Name; n Example: typedef unsigned int Uint; Uint tests[5]; // array of // unsigned ints

Uses of typedef n n Used to make code more readable Can be used to create alias for array of a particular type // Define year. Array as a data type // that is an array of 12 ints typedef int year. Array[12]; // Create two of these arrays year. Array high. Temps, low. Temps;

Arrays as Function Arguments n n To define a function that has an array parameter, use empty [] for array argument To pass an array to a function, just use the array name // Function prototype void show. Scores(int []); // Function header void show. Scores(int tests[]) // Function call show. Scores(tests);

Passing an Array Element n n Passing a single array element to a function is no different than passing a regular variable of that data type Function does not need to know the value it receives is coming from an array display. Value(score[i]); // call void display. Value(int item) // header { cout << item << endl; }

Passing an Entire Array n n Just use array name, without any brackets, as the argument Also pass array size so the function knows how many elements to process show. Scores(tests, 5); // call void show. Scores(int[], int); // prototype void show. Scores(int A[], int size) // header

Using typedef with a Passed Array n Can use typedef to simplify function prototype and heading // Make int. Array an integer array // of unspecified size typedef int. Array[]; // Function prototype void show. Scores(int. Array, int); // Function header void show. Scores(int. Array tests, int size)

Modifying Arrays in Functions n n n Array parameters in functions are similar to reference variables Changes made to array in a function are made to the actual array in the calling function Must be careful that an array is not inadvertently changed by a function

Two-Dimensional Arrays n Can define one array for multiple sets of data n Like a table in a spreadsheet n Use two size declarators in definition int exams[4][3]; Number of rows Number of cols

Two-Dimensional Array Representation int exams[4][3]; columns exams[0][0] exams[0][1] exams[0][2] r o w s exams[1][0] exams[1][1] exams[1][2] exams[2][0] exams[2][1] exams[2][2] exams[3][0] exams[3][1] exams[3][2] n Use two subscripts to access element exams[2][2] = 86;

Initialization at Definition n Two-dimensional arrays are initialized row-by-row int exams[2][2] = { {84, 78}, {92, 97} }; 84 78 92 97 n Can omit inner { }

Passing a Two-Dimensional Array to a Function n Use array name as argument in function call get. Exams(exams, 2); Use empty [] for row and a size declarator for col in the prototype and header // Prototype void get. Exams(int[][2], int); n // Header void get. Exams(int exams[][2], int rows)

Using typedef with a Two-Dimensional Array n Can use typedef for simpler notation typedef int. Exams[][2]; . . . // Function prototype void get. Exams(int. Exams, int); // Function header void get. Exams(int. Exams exams, int rows)

Arrays with Three or More Dimensions n Can define arrays with any number of dimensions short rect. Solid[2][3][5]; float time. Grid[3][4]; n When used as parameter, specify size of all but 1 st dimension void get. Rect. Solid(short [][3][5]);

Vectors n Defined in the Standard Template Library n n (STL) Covered in a later chapter Must include vector header file to use vectors #include <vector> n Holds a set of elements, like an array n But can grow and shrink in number of elements n n No need to specify size when defined Automatically adds space as more is needed

Vectors n Can hold values of any type n n Type is specified when a vector is defined vector<int> scores; vector<float> volumes; Can use [] to access elements

Defining Vectors n n Define a vector of integers (starts with 0 elements) vector<int> scores; Define int vector with initial size 30 elements vector<int> scores(30); Define 20 -element int vector and initialize all elements to 0 vector<int> scores(20, 0); Define int vector initialized to size and contents of another vector<int> scores(finals);

Growing a Vector’s Size n Use push_back member function to add an element to a full array or to an array that had no defined size // Add a new element holding a 75 scores. push_back(75); n Use size member function to determine number of elements currently in a vector howbig = scores. size();

Removing Vector Elements n Use pop_back member function to remove last element from vector scores. pop_back(); n To remove all contents of vector, use clear member function scores. clear(); n To determine if vector is empty, use empty member function while (!scores. empty()). . .

Arrays of Structures n Structures can be used as array elements struct Student { int student. ID; string name; short year; float gpa; }; Student class[30]; // Holds 30 Student // structures

Arrays of Structures n n Use array subscript to access a specific structure in the array Then use dot operator to access members of that structure cin >> class[25]. student. ID; cout << class[i]. name << " has GPA " << s[i]. gpa << endl;

Arrays of Class Objects n Class objects can also be used as array elements class Square { private: int side; public: Square(int s = 1) { side = s; } int get. Side() { return side; } }; Square shapes[10]; // Create array of 10 // Square objects

Arrays of Class Objects n n Use subscript to access a specific object in the array Then use dot operator to access members of that object for (i = 0; i < 10; i++) cout << shapes[i]. get. Side() << endl;

Initializing Arrays of Objects n n Can use default constructor to perform same initialization for all objects Can use initialization list to supply specific initial values for each object Square shapes[5] = {1, 2, 3, 4, 5}; n Default constructor is used for the remaining objects if initialization list is too short Square boxes[5] = {1, 2, 3};

Initializing Arrays of Objects n If an object is initialized with a constructor that takes > 1 argument, the initialization list must include a call to the constructor for that object Rectangle spaces[3] = { Rectangle(2, 5), Rectangle(1, 3), Rectangle(7, 7) };