1 Chapter 7 Arrays

2 Topics 7.1 Arrays Hold Multiple Values 7.2 Accessing Array Elements 7.3 No Bounds Checking in C Array Initialization 7.5 Processing Array Contents 7.6 Using Parallel Arrays

3 Topics 7.7 Arrays as Function Arguments 7.8 Two-Dimensional Arrays 7.9 Arrays of Strings 7.10 Arrays with Three or More Dimensions 7.11 Introduction to the STL vector

4 7.1 Arrays Hold Multiple Values An array allows you to store and work with multiple values of the same data type Array: variable that can store multiple values of the same type Values are stored in adjacent memory locations Declared using [] operator: int tests[5];

5 Array - Memory Layout The definition: int tests[5]; allocates the following memory: first element second element third element fourth element fifth element

6 Array Terminology In the definition int tests[5]; int is the data type of the array elements 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 (number of elements) * (size of each element)

7 Array Terminology The size of an array is: the total number of bytes allocated for it (number of elements) * (number of bytes for each element) Examples:

8 7.2 Accessing Array Elements Each array element has a subscript, used to access the element. Subscripts start at subscripts:

9 Accessing Array Elements Array elements can be used as regular variables: tests[0] = 79; cout << tests[0]; cin >> tests[1]; tests[4] = tests[0] + tests[1]; Arrays must be accessed via individual elements (except character array) : cout << tests; // not legal

10 Accessing Array Contents Can access element with constant subscript: cout << tests[3] << endl; Can use integer expression as subscript: for (i = 0; i < 5; i++) cout << tests[i] << endl;

11 Global vs. Local Array Global array  all elements initialized to 0 Local array  all elements uninitialized by default Examples: Program 7-1 Program 7-2

No Bounds Checking in C++ C++ does not check if an array subscript is in the range of values for subscripts of the array Can access memory using subscripts that is before or after the memory for an array Can corrupt other memory locations, crash program, or lock up computer

No Bounds Checking in C++ Example: Prog. 7-3Prog. 7-3

Array Initialization Can be initialized during program execution with assignment statements: tests[0] = 79; tests[1] = 82; // etc. Can be initialized at array definition with an initialization list: int tests[5] = {79,82,91,77,84}; Initialization list cannot exceed array size Examples: Prog. 7-4, Prog. 7-4 Prog. 7-5

15 Partial Array Initialization If array is initialized at definition with fewer initial values than the size declarator of the array, the remaining elements will be set to 0: int tests[5] = {79, 82}; Initial values used in order; cannot skip over elements to initialize noncontiguous range Example: Prog. 7-6Prog

16 Implicit Array Sizing Can determine array size by the size of the initialization list: short quizzes[]={12,17,15,11}; Must use either array size declarator or initialization list at array definition

17 Initializing With a String Character array can be initialized by enclosing string in " ": char fName[6] = "Henry"; Must leave room for \0 at end of array If initializing character-by-character, must add in \0 explicitly: char fName[6] = { 'H', 'e', 'n', 'r', 'y', '\0'}; Example: Prog 7-7Prog 7-7

Processing Array Contents Individual array elements are processed like any other type of variable Array elements can be treated as ordinary variables of the same type as the array When using ++, -- operators, don’t confuse the element with the subscript: tests[i]++; // add 1 to tests[i] tests[i++]; // increment i, no // effect on tests Example: Prog. 7-8Prog. 7-8

19 Array Assignment To copy one array to another, don’t try to assign one array to the other: newTests = tests; assign element-by-element: for (i=0; i<5; i++) newTests[i] = tests[i];

20 Display the Contents of an Array Can display character array by using its name: cout << fName << endl; For other types of arrays, must go element-by- element: for (i=0; i<5; i++) cout << tests[i] << endl;

21 Sum of Array Elements Use a simple loop to add together array elements: int tnum; float average, sum = 0; for(tnum = 0; tnum < 5; tnum++) sum += tests[tnum]; Once summed, can compute average: average = sum/5; Example: Prog 7-9Prog 7-9

Using Parallel Arrays Parallel Arrays: two or more arrays that contain related data Subscript is used to relate arrays: elements at same subscript are related Arrays may be of different types

23 Parallel Array Example string name[5]; // student name float average[5];// course average char grade[5]; // course grade... for(int i = 0; i < 5; i++) cout << "Student: " << name[i] << " average: " << average[i] << " grade: " << grade[i] << endl; Example Prog. 7-10Prog. 7-10

Arrays as Function Arguments Pass one element of an array to a function Example Prog. 7-11Prog To pass an array as an argument to a function, pass the name of the array: showScores(tests); To define a function that takes an array parameter, use empty [] for array argument: void showScores(int []); // function prototype void showScores(int tests[]) // function header

25 Arrays as Function Arguments When passing an array to a function, it is common to pass array size so that function knows how many elements to process: showScores(tests, 5); //function call Array size must also be reflected in prototype, header: void showScores(int [], int); // function prototype void showScores(int tests[], int size) // function header Examples Prog & Prog. 7-13Prog. 7-12Prog. 7-13

26 Modifying Arrays in Functions Array names in functions are similar to reference variables – changes made to array in a function are reflected in actual array in calling function Need to exercise caution that array is not inadvertently changed by a function Example Prog. 7-14Prog Useful array functions: total, average, highest, lowest, etc. Example Prog. 7-15Prog. 7-15

Two-Dimensional Arrays A two-dimensional array is like several identical arrays put together. It is useful for storing multiple sets of data. Can define one array for multiple sets of data Like a table in a spreadsheet Use two size declarators in definition: int exams[4][3]; First declarator is number of rows; second is number of columns

28 Two-Dimensional Array Representation int exams[4][3]; Use two subscripts to access element: exams[2][2] = 86; exams[0][0]exams[0][1]exams[0][2] 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] columns rowsrows

29 Initialization at Definition Two-dimensional arrays are initialized row- by-row: int exams[2][2] = { {84, 78}, {92, 97} }; Can omit inner { }, some initial values in a row – array elements without initial values will be set to 0 or NULL

30 Two-Dimensional Array as Parameter, Argument Use array name as argument in function call: getExams(exams, 2); Use empty [] for row, size declarator for column in prototype, header: void getExams(int [][2], int); // prototype void getExams(int exams[][2], int rows) // header

31 Examples Prog 7-16 Prog 7-17 Summing All the elements of a two-dimensional array The rows of a two-dimensional array The columns of a two-dimensional array The contents of table1 are: The contents of table2 are:

Array of Strings Use a two-dimensional array of characters as an array of strings: char students[3][10] = { "Ann", "Bill", "Cindy" }; Each row contains one string Can use row subscript to reference the string: cout << students[i];

Arrays with Three or More Dimensions Can define arrays with any number of dimensions: float seats[3][5][8]; When used as parameter, specify all but 1 st dimension in prototype, heading: void getRectSolid(short [][3][5]);

34 More About Array Array is passed by pointer Don’t want to change the contents of array: Insert const before the data type on the parameter lists in function prototype and function head Programmer Defined Data Type Using typedef in global section The programmer defined data type will show on the parameter lists in function prototype and function head Example Lab 5.1 Lab 5.3