CSE 113 Introduction to Computer Programming Lecture slides for Week 12 Monday, November 14 th, 2011 Instructor: Scott Settembre

COURSE ADMINISTRATION Section 1 Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 2

For Project Assistance You can find the up-to-date hours and locations in the “Contact” section of UBLearns. Here are the names, s, and office hours as of 11/14/2011: (Also come to additional labs if you need help) Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 3 Name addressOffice hours Bich (pronounced “Bic”) (11-11:50am) Bell 329 F (12-12:50pm) Bell 329 Troy (3-5pm) Bell 329 Scott (10-11am) Bell 232 F (10-11am) Bell 340 Also at all times by AND video conference by appointment.

You are behind the class if… If you have not: – completed chapter 1-6, then you are behind the rest of the class. – loaded the project 2 Greenfoot project and experiemented with a new AIMower class. Please do the following: – Begin working on project 2. – Start on chapter 7 in this week’s lab. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 4

Lecture and Lab this Week Lectures will go over the following: – Project 2 – switch statement – for loop Lab will have you do the following: – Start chapter 7. – Continue your project 2. – Lab Quiz on chapter 6 and Lecture notes from week 10 with for loops and switch statements. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 5

MIDTERM / FINAL EXAM / PROJECT Section 2 Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 6

Midterm exam (15%) The midterm exam will be held in lecture on October 21 st. It will cover chapters 1-6.4, including the exercises in the chapter that you do in lab. It will be a series of true/false, multiple choice, and code examination (running the code in your head), similar to the quizzes that you will have taken. Grades have been released. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 7

Final Exam (25%) The final exam will be during class during the last week of class. It will span two days, 45 minutes (or less) each day. It will consist of questions like the quizzes, as well as some code reading and understanding. More on this in November. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 8

Project 1 Project 1 grades have been posted. Good job! Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 9

Project 2 Due date: November 22 nd, 2011 at or before 11:59:59 PM We will design the abstract class we will be using in class, together. The project description will be discussed on Monday and Wednesday. The abstract class and Greenfoot project you will use will be distributed in lab. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 10

CHAPTER 6 Section 3 Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 11

The “for” loop Since counter loops are used so much, there is a quick and easy way to do them, the “for” loop. (sometimes called the “for..next” loop) Here is an example: for (int count=1; count <= 3; count++) { displayOutput("count == " + count); } displayOutput("Loop complete.“); Here is the output: count == 1 count == 2 count == 3 Loop complete. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 12

Components of a “for” loop You have the keyword “for” followed by an “expression” followed by a “statement” (or block). The expression contains 3 statements – First, a declaration or initialization that is run only once at the beginning of the loop. – Second, a Boolean expression or condition to evaluate to see if the loop should still run. – Lastly, an action to perform, usually an increment or iteration of some sort, performed at the end of the loop. “for” loops are quite nice to use as they cut down on the code clutter. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 13

Compare the “while” to “for” int count=0; while (count++ < 3) { displayOutput("count == " + count); } displayOutput("Loop complete."); for (int count=1; count < 3; count++) { displayOutput("count == " + count ); } displayOutput("Loop complete." ); Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 14

Collision Detection (not on test) Bounding-box Bounding-circle Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 15 Check each of the corners to see if it is inside another bounding box Make sure the two centers of each circle are greater than r1 + r2 away from each other

Collision Detection (not on test) Using masks – First, use bounding-boxes and determine all bounding-box collisions. – Second, take the masks from each sprite that had a bounding-box collision and see if they overlap. Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 16 It is fast to detect if rectangles overlap. It is slow to check before you set every pixel to see if it is part of the mask.

Drawing There are many Greenfoot commands that you can use to draw on the image of an Actor or the World. (Look at GreenfootImage class) Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 17

Easy way to draw on the background Get the World using getWorld() – (or if in the World class, just use “this”) Get the background image. – If in the World class, you would do use.getBackground() Draw a line. – If in an actor, you could write: getWorld().getBackground().drawLine(0,0,100,100); Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 18

Efficient Code Calling getWorld() and getBackground() each time you want to do something, can slow down performance. Try capturing the background in a private instance variable once, then using it later. – For example, in the class, make an instance variable private GreenfootImage myBackground; – Then in your constructor method or act method, you can: if (myBackground == Null) { myBackground = getWorld().getBackground(); } Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 19

Writing text // Get the background image, so we can write on it GreenfootImage scoreboard = getBackground(); // Clear what was written before scoreboard.setColor (new Color(0,153,0)); scoreboard.fillRect(0,0,120,40); // Change color to black, then write new info scoreboard.setColor(new Color(0,0,0)); scoreboard.drawString("Time: " + iterations++, 10, 10); Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 20

Objects and casting (more on this later) Objects may have more than one type! – For example, a “Dog” object is both of the “Dog” class and the “Animal” class and the “Actor” class. – If we want to make a list of Actors who are dogs and cats, we may say: List myPets; But then if one of the pets is of class “Cat”, then we will have a run-time error. Instead, we may the list like so: “List myPets;” Monday, Nov. 14th, 2011 University at Buffalo: CSE 113 Instructor: Scott Settembre 21