Karel J Robot Chapter 5

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

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

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

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

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

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

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

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

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

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

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

Chapter 5