1. Control Structures VB part 2
6-Jul-19

2. Overview
Control structures cause the program to repeat a section of code or choose between different sections of code
while loops repeat
if statements choose
Programs can use whiles and ifs in the Main method or in Jeroo methods
Control structures can use compound expressions to solve problems
Control structures can be nested inside each other to solve the most difficult problems

3. Using a while loop in a Jeroo method
Assume that a Jeroo named Kim is not standing on a flower, but there is a line of flowers ahead. Have Kim pick all of those flowers, and stop as soon as there is no flower directly ahead. After picking all of the flowers, Kim should turn to the left.
While Kim.isFlower(AHEAD)
Kim.hop()
Kim.pick()
End While
Kim.turn(LEFT)
How would this be written as part of a method?

4. While isFlower(AHEAD) hop() pick() End While turn(LEFT) End Sub
As part of a method
Sub pickRow()
While isFlower(AHEAD)
hop()
pick()
End While
turn(LEFT)
End Sub
The main program would be:
Sub Main()
Dim Kim as Jeroo = new Jeroo()
Kim.pickRow()
End Sub

5. Review: The Conditional statements
some statement
if condition THEN
do if true
End If
next statement
some statement
if (condition) Then
do if true
else
do if false
End If
next statement
If condition_1 then
'statements that execute if condition_1 is true
elseif condition_2 then
'statements to execute when condition_2 is true
'more else if blocks as necessary
elseif last_condition then
'statements to execute when last_condition is true
else
'statements to execute when
all conditions are false
End If If
If-else
Cascaded if

6. Changing Cascaded-If into a Jeroo method
Sub Decide()
Assume that a Jeroo named Louisa is carrying at least one flower.
Have her check the cell ahead.
If that cell contains a flower, pick it.
If that cell contains a net, disable it.
If that cell contains water, plant a flower at the current location.
If that cell contains another Jeroo, give that Jeroo a flower.
Finally, if there is nothing in that cell, have her hop once and turn left.
if Louisa.isFlower(AHEAD) then
Louisa.hop()
Louisa.pick()
elseif Louisa.isNet(AHEAD) then
Louisa.toss()
elseif Louisa.isWater(AHEAD) then
Louisa.plant()
elseif Louisa.isJeroo(AHEAD) then
Louisa.give(AHEAD)
else
Louisa.turn(LEFT)
End If
End Sub
To turn this into a Jeroo method, give it a name and remove the specific Jeroo name from the code

7. Simple and Compound Conditions
A simple condition has one part. In the Jeroo language, a simple condition is formed by invoking a single sensor method.
Examples:
Tiffany.isClear(right)
Walter.isFacing(East)
A compound condition uses logical operators. The Jeroo language contains the three most commonly used logical operators:
NOT ie: NOT Tiffany.isClear(right)
AND ie: Tiffany.isClear(right) AND Tiffany.isClear(left)
OR ie: Tiffany.hasFlower() OR Tiffany.isClear(ahead)

8. Compound condition examples
Boolean Expression (VB-style) & English Translation
NOT Bob.isNet(AHEAD)
There is not a net ahead of Bob
Bob.hasFlower() AND Bob.isClear(LEFT)
Bob has at least one flower and there is nothing in the cell immediately to the left of Bob.
Bob.isWater(AHEAD) OR Bob.isWater(RIGHT)
There is water ahead or to the right of Bob, or both
Notice the COMPLETE CONDITIONS on both sides of the OR
Bob.isFacing(WEST) AND ( NOT Bob.isNet(AHEAD) )
Bob is facing west and there is no net ahead
Use these examples to write compound conditions

9. A more complex Programming Example
Have the Jeroo named Jessica (who has at least 1 flower) keep moving forward until she finds a net to her left or right. When she finds one, have her disable it and return to face her original direction again. After she disables a net, Jessica should hop one space ahead.
Pseudocode:
While there is not a net on the left or right
hop
End While
If there is a net to the right then
disable the net on the right and turn back
Else ‘ if the net is not to the right, it must be on the left
disable the net on the left and turn back
End If
hop one time
first keep hopping until a net is found
then disable the net, whichever side it is on
then hop once

10. Translate the pseudo code to code
While there is not a net on the left or right
hop
End While
If there is a net to the right then
disable the net on the right and turn back
Else ‘ if the net is not to the right, it must be on the left
disable the net on the left and turn back
End If
Jessica.hop()
first problem
Which is the correct way to say:
“there is not a net on the left or right” ?
NOT isNet(left) OR isNet(right)
NOT isNet(left) and NOT isNet(right)
this can be read as: there is not a net on the left and there’s not a net on the right.

11. Translate the pseudo code to code
While there is not a net on the left or right
hop
End While
If there is a net to the right then
disable the net on the right and turn back
Else ‘ if the net is not to the right, it must be on the left
disable the net on the left and turn back
End If
Jessica.hop()
this has been solved before
so how must it change if the net is on the left?
turn(RIGHT)
toss()
turn(LEFT)
turn(LEFT)
toss()
turn(RIGHT)

12. Put it together: Which part still needs to be translated into code?
While NOT isNet(left) and NOT isNet(right)
hop()
End While
If there is a net to the right then
Else ‘ if the net is not to the right, it must be on the left
End If
Jessica.hop()
isNet(right) then
turn(RIGHT)
toss()
turn(LEFT)
turn(LEFT)
toss()
turn(RIGHT)
Ready to type in the code!
Is this code for a Main method or a Jeroo method? Why?
The code does not specify a Jeroo name, so it belongs in a Jeroo method

13. Control structures can be nested inside each other to solve the most difficult problems

14. A problem requiring nested control structures
Remove all the nets on Jessica’s right side as she hops all the way across the island.
The code to remove one net and move forward has already been written:
If isNet(RIGHT) then
turn(RIGHT)
toss()
turn(LEFT)
End If
hop()

15. Some questions: Answer: Question:
The Problem: Remove all the nets on Jessica’s right side as she crosses the island.
Answer:
there is water ahead
While NOT iswater(ahead)
hop()
End While
‘ put the code here to
‘ remove a net if there is one.
Question:
How do you know that a Jeroo has reached the end of the island?
How do you say “ keep hopping until you reach the end of the island”?
How do you say “keep removing nets until you reach the end of the island”?

16. Final version: Put the pieces together
Notice the indentation:
While not iswater(ahead)
‘ remove the net if there is one.
If isNet(RIGHT) then
turn(RIGHT)
toss()
turn(LEFT)
End If
hop()
End While

17. The End