1. Karel J Robot
Chapter 5

2. Chapter 5 Conditional Statements
Flavor 1:
if ( <some boolean expression> ) {
<some instruction list> }
For now: these are method invocations (see next slide)
Chapter 5

3. IF frontIsClear(); nextToABeeper(); nextToARobot(); facingNorth();
“predicates”
either T or F IF
frontIsClear();
nextToABeeper();
nextToARobot();
facingNorth();
facingSouth();
facingEast();
facingWest();
anyBeepersInBeeperBag();
if ( ) { … }
Robot
Chapter 5

4. again, you don’t write this class
Robot Class
public class Robot extends UrRobot {
public boolean frontIsClear() {…}
public boolean nextToABeeper() {…}
public boolean nextToARobot() {…}
etc… }
Now I have a brain!
again, you don’t write this class
Chapter 5

5. Examples if (frontIsClear() ) { move(); // no danger of hitting wall }
if ( anyBeepersInBeeperBag() ) {
putBeeper(); // no danger of error }
Chapter 5

6. public boolean beeperIsToLeft() { turnLeft(); move();
MUST put world back in initial situation that it was in BEFORE the method was invoked
public boolean beeperIsToLeft() {
turnLeft();
move();
if ( nextToABeeper() )
turnLeft(); turnLeft(); move(); turnLeft(); return true; }
turnLeft(); turnLeft(); move(); turnLeft();
return false;
Chapter 5

7. Boolean Operators Karel (Java) Robot (&&, ||, !) if (! frontIsClear()){
turnLeft(); }
move();
Chapter 5

8. IF - ELSE Flavor 2: if ( <boolean expression> ) {
<statements> }
else
<statements – somewhat different>
Chapter 5

9. IF – ELSE Simplifications
simplify:
if ( frontIsClear() ) {
return true; }
return false;
simplify:
if ( frontIsClear() ) {
return true; }
else
return false;
Chapter 5

10. Simplify – bottom factoring
move();
move();
if ( facingSouth() ) {
turnLeft();
move(); }
else
turnRight();
if ( facingSouth() ) {
turnLeft(); }
else
turnRight();
move();
move();
move();
move();
Chapter 5

11. Simplify – top factoring
move();
if ( beeperOnLeft() ) {
turnLeft(); }
else
turnRight();
if ( beeperOnLeft() ) {
move();
turnLeft(); }
else
turnRight();
Chapter 5

12. no need to check for the same thing twice!
if ( facingNorth() ) {
move();
pickTwoBeepers();
if (facingNorth())
turnLeft(); }
if ( facingNorth() ) {
move();
pickTwoBeepers();
turnLeft(); }
Chapter 5

13. Chapter 5