Download
comp 14 introduction to programming n.
Skip this Video
Loading SlideShow in 5 Seconds..
COMP 14 Introduction to Programming PowerPoint Presentation
Download Presentation
COMP 14 Introduction to Programming

COMP 14 Introduction to Programming

204 Vues Download Presentation
Télécharger la présentation

COMP 14 Introduction to Programming

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. COMP 14Introduction to Programming Adrian Ilie July 14, 2005

  2. Arrays • 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 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.

  4. counter characterSet grade Declaring ArraysExamples // array of counters (integers) int[] counter; // array of characters char[] characterSet; // array of grades (doubles) double[] grade;

  5. Instantiating Arrays 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= newtype[size]; The array (element) data type The number of elements

  6. counter 0 1 2 3 4 Instantiating ArraysExamples // instantiate an array of counters counter = new int[5]; 0 <= index < size // instantiate the array of grades numStudents = 10; grade = new double[numStudents];

  7. Declaration Instantiation Declaration and Instantiation type[]name= new type[size];

  8. Example int[] num = new int[5];

  9. Array AccessExamples 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; totalScore = 0; for (int i = 0; i < numStudents; i++) { totalScore += score[i]; } averageScore = totalScore/numStudents; often use loops for access

  10. Array Length 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]; }

  11. Initializing Arrays • 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.

  12. Initializer Lists • 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};

  13. Array Bounds • 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]);

  14. Example Specify Array Size During Program Execution (Assume thatkeyboard has already been declared and instantiated.) intarraySize; System.out.print ("Enter the size of the array:"); arraySize = Integer.parseInt(keyboard.readLine()); int[] list =new int[arraySize];

  15. Example 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; }

  16. Example Read Data into Array (Assume that sale has already been declared and instantiated, and thatkeyboard has already been declared and instantiated.) for (int ind = 0; ind < sale.length; ind++) { sale[ind] = Double.parseDouble(keyboard.readLine()); }

  17. Example Print Array (Assume that sale has already been declared and instantiated.) for (int ind = 0; ind < sale.length; ind++) { System.out.print(sale[ind] + " "); }

  18. Parallel Arrays 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].

  19. In-Class Exercises • Declare an array of integers called numbers • Declare and instantiate an array of 26 characters called alphabet

  20. In-Class Exercises • Declare an array of 5 characters called grades and initialize it with the letters: A, B, C, D, F Hint: type[] name = {initialization list}; • Write a loop to print the contents of an array named zipCodes Hint: to access array elementname[index]

  21. In-Class Exercises • Write a loop to change all the values of the integer array numbersto index + 1

  22. Exercises 1. Find Sum and Average of Array 2. Determine Largest and SmallestElements in Array

  23. Homework 6 (practice) • Read data from file • Fill arrays with data • Fill objects with data

  24. Tomorrow • More Arrays • arrays of objects • passing arrays as parameters • searching and sorting • Homework 5 due Sunday midnight • Bring laptops!!!