While loops – weeks 13 and 14

“Just keep swimming… just keep swimming…”

-Dory

Handout: 7_intro_1_while_loops

the While loop

A solution using While loops Show it to me

A solution with a while loop is short, clear, does not waste cycles, and does not waste memory: it stops as soon as the goal is accomplished.

Recursion and while loops do the same thing; they just do it in different ways. A solution to a problem that uses recursion is called recursive; a solution that uses a loop is called iterative.

The iterative solution is not as elegant as the recursive solution but since an iterative solution does not need to make multiple copies of a function, like the recursive does, is usually faster and always less expensive in terms of memory.

TM1 go to a wall

Let me try

Please, write the iterative function go_to_wall() that moves Karel to a wall in front of him.


go_to_wall() - 0
steps = 0


go_to_wall() - 1
steps = 1


go_to_wall() - 2
steps = 2


go_to_wall() - 3
steps = 3


Answer: show it to me

This is easy:

3rd grade – Pave the way

Work it out

Please, use a while loop to pave the 5 steps in front of Karel’s house.

away-763918_640

Answer: Show it to me


Ready!

Ready!


all done.

all done.


4th grade – Every steps counts

Work it out

Write an program using while loops that gets Karel to score a touchdown, i.e., have him pick up the first ball he finds and then run to the end zone.

football-671224_640

Answer: Show it to me


Before: Ready!

Before: Ready!


and after

and after


5th grade – Strawberries – Reaping what you sow

Work it out


It is summer and the strawberry plants are starting to give fruit. Sweet… have Karel collect all the strawberries on his way home that is somewhere in front of him..


berry-197078_640


Answer: Show it to me


Ready to collect my strawberries

Ready to collect my strawberries


Yummy

Yummy


6th grade – The rooms of doom – In the belly of the sphinx

Work it out

egypt-518584_640The strategy here is the following. Every cell of the room has a stack of 1 to 6 tokens. Karel has to count the tokens; if the result is..

..an even number (i.e., 2, 4, or 6.), turn right
..an odd number (i.e., 1, 3 or 5), turn left

and move forward by that number to the next stack of tokens.

For example, if Karel finds a stack with 4 tokens he has to turn right and move 4 steps to a cell where he will find the next stack.

This procedure will take us to the home square, in which we will find the star.

Karel starts with an empty bag. We provide you with a function that returns the number tokens of the cell on which Karel is standing.

Answer: Show it to me

I'm scared...

I’m scared…

Woot!

Woot!