Karel J Robot

1. Karel J Robot Chapter 6

2. What we have learned so far: • Classes vs objects (e.g. UrRobot vs. karel) • Parts of a class (constructor, method) • Classifying errors • Polymorphism (extending classes) • Abstract classes and interfaces • Conditionals • Booleans, logical operators

3. For Loop • Loops – code that repeats some action either a finite or infinite amount of times • Also called iteratives • 2 types of loops • Definate loops (for) perform instructions an explicit number of times • Indefinate loops (while) perform instructions until a certain test fails

4. For Loop • Example: public void move(intnumMoves){..} • Which loop do we want? • Structure of a for loop: • For(int x = 0; x<10; x++) • { <repeated code>} • For loop needs 3 things: • An initializer – can be initialized in for loop, or before • A boolean test – loop while run until the test is false • An operation – typically an incrementer

5. For Loop • How many times will each for-loop run? • for(x=0; x<10; x++) { …} • for(x=0; x<=10; x++){…} • for(x=10; x>0; x--){…} • for(x=2; x>=14; x+=2) {…} • Feel free to program the code and test it • Let’s keep to a standard form: • Start: x=0; • Test: x<#; //don’t use <=; the # will represent how many times the loop runs • Increment by x++;

6. While Loop • Aside: the For-Loop takes on different forms, but the previous slides demonstrate its simplest form • For Loop – good for looping when you know how many times you need to repeat • When you need to program a loop that runs until a certain event happens…. Use a while loop

7. While Loop • Form: • while(<test>) • { <do instructions>} • Examples: • while(!nextToABeeper()) {..} • while(x>10){…} • while(2>=4){…} • The test can be any boolean outcome • The actions in the loop should make progress to change the boolean test (to avoid an infinite loop)

8. Relational Operators • Review • ->Logical operators: &&, ||, ! • Relational Operators are used for comparison • >, >=, < <=, ==, != • Note: = and == are not the same thing! = is the assignment operator… == is ‘equal to’

9. Student work • Read chapter 6 (up to page 161) • Program the Guard robot on page 162 to the end of the chapter • Problem set 6 • #1,2,3,8,14,16,24,34