2B: Loops

Loops let you repeat sections of your code. They’re a great shortcut — without them, you might have to write the same lines over and over again.

In this lesson, you’ll be learning about while loops and for loops. Both of them are conditional loops, so they repeat only for as long the condition that you set is true.

To keep track of how many times we repeat our code in the loop, we need to have a way for the computer to count. So first, let’s think about how humans count!

We pick a starting number, then keep increasing the number by 1 until we reach the number we want to reach.

We can keep track of values in our brain, but computers will need variables! As you saw in the last lesson, variables are placeholders that can be assigned a value. Just like we set a starting number for counting, let’s initialize our count variable to 1 and count to 4. Run this code to see what happens!

count = 1

while count < 5:
    print(count)
    count = count + 1

This is a while loop in Python. But let’s break it down.

While loops repeat a set of code while a condition you set is true. You use these in your life all of the time! This is what they look like:

while condition(s) go here:
    statements goes here

In English, you could hear an example like this: As long as my phone has battery, I will go on Instagram. But in code it would like this:

while phone has battery:

    I will use Instagram

For this while loop to initiate, the condition needs to be true. Else, it will be skipped. As long as the conditions are true, the statements will run over and over. When the condition becomes false, the program will exit out of the loop and continue on to the rest of the program

Program your CoDrone Mini to do pushups using a while loop. Have the condition be true only until a variable passes 10.

import CoDrone_mini

drone = CoDrone_mini.CoDrone()

drone.pair()


pushups = 0

while pushups < 10:

    drone.takeoff() 

    drone.hover(1)

    drone.land() 

    pushups+=1       # increment pushups by 1

drone.close()

P.S.: While loops can go on forever if you set the condition in the while loop to be “1” or “True”.

For loops are a lot like while loops — they repeat lines of code while a condition is true. However, the condition is a specific number of times that you set. For example, if you only wanted your line of code to repeat 87 times, you would use a for loop.

The conditional statement for a for loop follows a very specific format that looks intimidating, but we’ll break it down!

for private variable in range (minimum, maximum, increment or decrement):

    Write statements here

• Private variables are variables that you only use for the loop and nothing else.
• The minimum is the value that your variable will start at.
• The maximum is the value that your variable will end at.
• Increment is how much will be added to your variable every time, and decrement is how much will be subtracted from your variable every time.

Here’s an example:

for x in range(0, 10, 1):

    print(x)

• The private variable is x.
• x will start out at 0.
• The limit for this range is 10.
• x will increase by 1 every time the program goes through the loop. With the first iteration, x starts at zero, print “ 0 “, and then x becomes 1. In the second iteration, x starts at 2, prints “1”, and then becomes 2. The console, where results are printed, should show the following:

0

1

2

3

4

5

6

7

8

9

Did you see that “10” wasn’t printed? That’s because it was the maximum limit. When the private variable, which is x in our example, reaches the maximum limit, it does not print it or go past it.

You can also move in the negative and decrement, or decrease. Here’s an example:

for j in range(-1, -13, -2):

    print(j)

What do you think the results look like? Write them down before looking at the next part!

Program your CoDrone to fly in a square. Remember that computers start counting at 0 and 4 is the maximum.

import CoDrone_mini

drone = CoDrone_mini.CoDrone()

drone.pair()


drone.takeoff()

for x in range(0, 4, 1):

    drone.set_pitch(50)   

    drone.move(2) 

    drone.set_pitch(0)    

    drone.set_yaw(-50)   

    drone.move(2)

    drone.set_yaw(0)      

drone.land()

drone.close()

Next, try other shapes, like triangles, pentagons, and hexagons!

Have the CoDrone Mini do 5 pushups and print the following messages: “taking off”, “hovering”, and “landing”.

Try making one version using a for loop and another using a while loop.

Challenge: Tower of Terror

The Tower of Terror at a few of the Disney parks is a drop tower ride. These rides typically take riders up very high and very slowly, and then drop down very quickly. With a lot of drop tower rides, the riders go down, pause, go up a little bit but not that high, pause, go down, pause…you get it.

Your challenge is to use loops to program your CoDrone Mini to fly in the same pattern as the Tower of Terror!

Rules:

• You must use either a for or while loop.
• Your drone, after going up, must go down, pause, go up, and then pause at least three times.

One example:

import CoDrone_mini

drone = CoDrone_mini.CoDrone()

drone.pair()


drone.takeoff() 

drone.set_throttle(50)

drone.move(2)

drone.hover(1)


for x in range(0, 5, 1):

    drone.set_throttle(50)

    drone.move(2)

    drone.hover(1)

    drone.set_throttle(-40)

    drone.move(2)

    drone.hover(1)

    
drone.land()

drone.close()