COMP 14 Introduction to Programming Miguel A Otaduy June 1 2004 Arrays 0 1 2 An array is a list of values that can be represented by one variable Members of an array must all have the same data type Each value is stored at a specific numbered position in the array the number corresponding to each position is called an index or subscript All arrays have a length number of elements the array can hold 3 Declaring Arrays 0 1 2 The array element data type Empty square brackets type name The array variable name Creates a reference variable called name that can point to an array of type elements 3 Declaring Arrays 0 1 2 Examples array of counters integers int counter array of characters char characterSet array of grades doubles double grade counter characterSet grade 3 0 1 Instantiating Arrays 2 3 You must instantiate create arrays the size of an array is typically not known before run time The assignment operator The array variable name The new operator name new type size The array element data type The number of elements 0 1 Instantiating Arrays 2 3 Examples instantiate an array of counters counter new int 5 0 index size 0 1 2 3 4 instantiate the array of grades numStudents 10 grade new double numStudents counter Declaration and Instantiation 0 1 2 type name new type size Declaration Instantiation 3 Example 0 1 int num new int 5 2 3 Array Access 0 1 2 3 Examples double score new score 3 score 0 98 3 score 1 57 8 score 2 93 4 averageScore score 0 score 1 score 2 3 numStudents 3 often use loops for access totalScore 0 for int i 0 i numStudents i totalScore score i averageScore totalScore numStudents Array Length 0 1 2 Arrays have length an internal variable called length number of elements in array access the length variable using the dot notation arrayname length loop through the array of test scores sumOfScores 0 for int i 0 i scores length i sumOfScores scores i 3 Initializing Arrays 0 1 2 3 Array elements are variables too if you don t initialize the contents are undefined When and how if you don t yet know the size initialize at run time typically with a loop if you know how many elements perhaps use an initializer list int counter 0 0 0 0 0 char characterSet a b c etc Initializer Lists 0 1 2 3 List the initial value for the elements of an array Items are separated by commas and the list is in braces The size of the array is determined by the number of items in the list int scores 87 98 45 Can only be used in the same statement as declaring the array NOT int scores scores 87 98 45 Array Bounds 0 1 2 3 Arrays have finite size If you access an element outside of the array you ll get an ArrayIndexOutOfBounds Exception Example int grades 99 98 95 96 System out println grades 4 Example 0 1 2 3 Specify Array Size During Program Execution Assume that keyboard has already been declared and instantiated int arraySize System out print Enter the size of the array arraySize Integer parseInt keyboard readLine int list new int arraySize Example 0 1 2 3 Initialize Array to Specific Value 10 00 Assume that sale has already been declared and instantiated for int ind 0 ind sale length ind sale ind 10 00 Example 0 1 2 3 Read Data into Array Assume that sale has already been declared and instantiated nd that keyboard has already been declared and instantiated for int ind 0 ind sale length ind sale ind Double parseDouble keyboard readLine Example 0 1 2 3 Print Array Assume that sale has already been declared and instantiated for int ind 0 ind sale length ind System out print sale ind Parallel Arrays 0 1 2 Arrays are parallel if corresponding components hold related information String studentName double studentGPA For example studentName and studentGPA are parallel if studentGPA 3 is the GPA of the student with studentName 3 3 In Class Exercises 0 1 2 1 Declare an array of integers called numbers 2 Declare and instantiate an array of 26 characters called alphabet 3 In Class Exercises 3 0 1 2 Declare an array of 5 characters called grades and initialize it with the letters A B C D F Hint type name initialization list 4 3 Write a loop to print the contents of an array named zipCodes Hint to access array element name index In Class Exercises 0 1 2 3 5 Write a loop to change all the values of the integer array numbers to index 1 Exercises 0 1 1 Find Sum and Average of Array 2 Determine Largest and Smallest Elements in Array 2 3 Homework 6 practice Read data from file Fill arrays with data Fill objects with data Tomorrow More Arrays arrays of objects passing arrays as parameters searching and sorting Homework 5 due Wednesday midnight Homework 6 assigned Bring laptops