CS 104 – Fall 2011 Exploring Computer Science

1. CS 104 – Fall 2011Exploring Computer Science Lecture 20: November 14, 2011 Procedural Abstraction and List Processing

2. Schedule • Today • Procedural Abstraction in App Inventor • List Processing in App Inventor • High Score List Processor • Wednesday • No quiz • Return quizzes 5 and 6; last team homework • Big Data Lecture • Storing Databases • Next Monday • Exam 2 • Focus on App Inventor

3. General Idea • Project example for today • Allow the user to enter high scores • Maintain a list of the top-5 highest scores • Requirements • Procedure to initialize a list • Procedure to insert a new score into the proper location • Procedure to print contents of list to a textbox

4. List Processing • Lists in App Inventor are similar to those in BYOB • Creating a list, selecting/replacing/removing/inserting • Functions for checking membership, location of an item, contents empty • An error when going beyond the size of a list

5. Iterating over a list • App Inventor offers the forRange and forEach control constructs

6. App Inventor Procedures • App Inventor provides procedures that can receive arguments, and either return a result (like BYOB reporter) or not return a result (like BYOB command)

7. High Score List Keeper • Variable declarations and simple events

8. High Score List Keeper • insertItem

9. High Score List Keeper