CMSC 150CONDITIONALEXECUTION

CS 150: Mon 16 Jan 2012

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

Java executes statementsstep-by-stepin exactly the

orderyou have them

6

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

7

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

8

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

9

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

10

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

11

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

12

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

13

Sequential Executionimport java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

14

How Is This Different?import java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “Enter sphere radius:“ ); System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

15

How Is This Different?import java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

double radius = keyboard.nextDouble();

double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius;

System.out.println( “Enter sphere radius:“ ); System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

16

Now, How Is This Different?import java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double volume = (4.0 / 3.0) * pi * radius * radius * radius; double pi = 3.14159;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

17

Now, How Is This Different?import java.util.Scanner;

public class ProgramFive {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble();

double volume = (4.0 / 3.0) * pi * radius * radius * radius; double pi = 3.14159;

System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume );

}}

Will not compile!

Trying to use a variable before it

is declared

18

Find the Runtime Errorimport java.util.Scanner;

public class ExampleProgram {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter an integer:” ); int firstNumber = keyboard.nextInt();

System.out.println( “Enter another integer:” ); int secondNumber = keyboard.nextInt();

double ratio = (double) firstNumber / secondNumber;

System.out.println( “The ratio is “ + ratio );}

}

19

Find the Runtime Errorimport java.util.Scanner;

public class ExampleProgram {

public static void main(String[] args){

Scanner keyboard = new Scanner( System.in );

System.out.println( “Enter an integer:” ); int firstNumber = keyboard.nextInt();

System.out.println( “Enter another integer:” ); int secondNumber = keyboard.nextInt();

double ratio = (double) firstNumber / secondNumber;

System.out.println( “The ratio is “ + ratio );}

}

potentially…

20

Java will execute the statement only if the condition is

true

Conditional Execution

// lots of your great code…if ( condition ){ statement;} …// lots more of your great code

21

// lots of your great code…double ratio = 0.0;if ( secondNumber != 0 ){ ratio = (double) firstNumber / secondNumber;} …// lots more of your great code

Conditional Execution

a Boolean condition

22

// lots of your great code…double ratio = 0.0;if ( secondNumber != 0 ){ ratio = (double) firstNumber / secondNumber;} …// lots more of your great code

Conditional Execution

Java will compute the ratio

only if the condition is true

(i.e., non-zero second #)

23

// lots of your great code…double ratio = 0.0;if ( secondNumber != 0 ){ ratio = (double) firstNumber / secondNumber;} …// lots more of your great code

Note The Difference…// lots of your great code…

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber;} …// lots more of your great code

24

// lots of your great code…double ratio = 0.0;if ( secondNumber != 0 ){ ratio = (double) firstNumber / secondNumber;} …// lots more of your great code

Note The Difference…// lots of your great code…

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber;} …// lots more of your great code

the variable ratio will not be accessible

outside the if statement!

25

Conditions Boolean expressions Must evaluate to true or false

Comparison operators: ==, <, >, <=, >=, !=

Compound expressions: Logical and: && Logical or: || Logical not: !

26

Truth Tables

P Q P && QT T TT F FF T FF F F

P Q P || QT T TT F TF T TF F F

P !PT FF T

P, Q can be any Boolean expression (perhaps compound)

27

Compound Expressions firstNumber == 0 && secondNumber == 0

firstNumber < 0 && secondNumber < 0

firstNumber > 0 && !(secondNumber > 0)

firstNumber == 0 || secondNumber == 0

firstNumber < 0 && firstNumber > 0

firstNumber < 0 || firstNumber > 0

!( firstNumber == 0 || secondNumber == 0 )

28

If / If-Else / If-Else-If if ( condition )

{ statement; }

if ( condition ){ statement; }else{ statement;}

if ( condition ){ statement; }else if ( condition ){ statement; }else{ statement;}

29

Understanding Conditionalsif ( secondNum != 0 )

{

ratio = firstNum / secondNum;

}

else

{

System.out.println(

“Divide by zero!” );

}

if ( secondNum != 0 )

{

ratio = firstNum / secondNum;

}

if ( secondNum == 0 )

{

System.out.println(

“Divide by zero!” );

}

30

Understanding ConditionalsString sign;

if ( number == 0 )

{

sign = “non-negative”;

}

else if ( number < 0 )

{

sign = “negative”;

}

else if ( number > 0 )

{

sign = “positive”;

}

String sign;

if ( number == 0 )

{

sign = “non-negative”;

}

if ( number < 0 )

{

sign = “negative”;

}

if ( number > 0 )

{

sign = “positive”;

}

31

Understanding ConditionalsString sign;

if ( number == 0 )

{

sign = “non-negative”;

}

else if ( number < 0 )

{

sign = “negative”;

}

else

{

sign = “positive”;

}

String sign;

if ( number == 0 )

{

sign = “non-negative”;

}

if ( number < 0 )

{

sign = “negative”;

}

else

{

sign = “positive”;

}

32

Understanding ConditionalsString sign;

if ( number == 0 )

{

sign = “non-negative”;

}

else if ( number < 0 )

{

sign = “negative”;

}

else

{

sign = “positive”;

}

String sign;

if ( number == 0 )

{

sign = “non-negative”;

}

if ( number < 0 )

{

sign = “negative”;

}

else

{

sign = “positive”;

}

33

Understanding ConditionalsString sign;

if ( number == 0 )

{

sign = “non-negative”;

}

else if ( number < 0 )

{

sign = “negative”;

}

else

{

sign = “positive”;

}

String sign;

if ( number == 0 )

{

sign = “non-negative”;

}

if ( number < 0 )

{

sign = “negative”;

}

if ( number > 0 )

{

sign = “positive”;

}

34

Compound Statements if ( condition )

{ statement; statement; statement; … }

if ( condition ){ statement; statement; statement; … }else{ statement; statement; statement; …}

To Java, this isa single

statement

35

Compound Statements if ( condition )

{ statement; statement; statement; … }

if ( condition ){ statement; statement; statement; … }else{ statement; statement; statement; …}

Statements inside can be anything…

Even another if statement!

36

Nested Conditionals if ( condition_1 )

{ if ( condition_2 ) { statement_1; } else { statement_2; }}

37

Nested Conditionals if ( condition_1 )

{ if ( condition_2 ) { statement_1; } else { statement_2; }}

if ( condition_1 && condition_2 ){ statement_1;}

if ( !condition_2 ){ statement_2;}

38

Nested Conditionals if ( condition_1 )

{ if ( condition_2 ) { statement_1; } else { statement_2; }}

if ( condition_1 && condition_2 ){ statement_1;}

if ( !condition_2 ){ statement_2;}

39

Nested Conditionals if ( condition_1 )

{ if ( condition_2 ) { statement_1; } else { statement_2; }}

if ( condition_1 && condition_2 ){ statement_1;}

if ( condition_1 && !condition_2 ){ statement_2;}

40

firstNumber

Changing The Flow...

System.out.println( “Enter another integer:” );int secondNumber = keyboard.nextInt();

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio );}else{ System.out.println( “Divide by zero error!” );}

...

secondNumber

21

7

41

Changing The Flow...

System.out.println( “Enter another integer:” );int secondNumber = keyboard.nextInt();

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio );}else{ System.out.println( “Divide by zero error!” );}

...

firstNumber

secondNumber

21

7

42

Changing The Flow...

System.out.println( “Enter another integer:” );int secondNumber = keyboard.nextInt();

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio );}else{ System.out.println( “Divide by zero error!” );}

...

firstNumber

secondNumber

21

7

ratio 3

43

Changing The Flow...

System.out.println( “Enter another integer:” );int secondNumber = keyboard.nextInt();

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio );}else{ System.out.println( “Divide by zero error!” );}

...

firstNumber

secondNumber

21

7

ratio 3

44

firstNumber

Changing The Flow...

System.out.println( “Enter another integer:” );int secondNumber = keyboard.nextInt();

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio );}else{ System.out.println( “Divide by zero error!” );}

...

secondNumber

21

0

45

Changing The Flow...

System.out.println( “Enter another integer:” );int secondNumber = keyboard.nextInt();

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio );}else{ System.out.println( “Divide by zero error!” );}

...

firstNumber

secondNumber

21

0

46

Changing The Flow...

System.out.println( “Enter another integer:” );int secondNumber = keyboard.nextInt();

if ( secondNumber != 0 ){ double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio );}else{ System.out.println( “Divide by zero error!” );}

...

firstNumber

secondNumber

21

0

47

Let’s Hunt The Wumpus48

Our Maze

PIT

49

Our RulesPIT

Player can move one step per turn up, down, left, or right cannot move off the maze (grid)

Find the gold win Find the wumpus lose Find the pit lose a turn

Player gets only four turns, otherwise draw

50

Location In The Maze

PIT

0 1 2

0

1

2

51

Handle Player Movement First…

0 1 2

0

1

2

52