2C: Conditionals

If statements are conditionals, which are used to help your program make decisions. You actually use conditionals every day! Some examples might include:

1. If my alarm goes off, then I will wake up. Else, I will stay asleep.
2. If I am hungry, I will eat something.
3. If it’s sunny out, I will wear sunscreen.
4. If my room is clean, I will get my allowance. Else, I will make no money.

If statements in Python are written like this:

if insert condition here:

     Insert statements here

else:

     Insert statements here

See what they look like in our example:

if alarm goes off:

     I will wake up

else:

     Stay asleep

• The condition is what the computer checks to know if it is true or false.
• If the condition is true, the computer will execute the statements underneath it.
• If the condition is false, the computer will NOT execute the statements underneath it.
• “Else” has no condition. This is because “else” is the last option when using if-else statements.  When a computer reaches the “else” option after checking all the other conditions, the else condition is automatically true and will run its statements.
• One way to use “else” would be when something needs to happen when a condition is false. When the if condition is false and nothing needs to happen, you don’t need to use an “else”.

Indentation is very important in Python. The indentations indicate which statements belong to a particular section in the code.

You may have noticed that the statements below the if and else statements are indented 4 spaces or one tab. If you want to have multiple statements executed if a condition is true using proper indentation, it would look like this:

if battery_percentage > 60:

    print("Ready for takeoff!")

    drone.takeoff()

    drone.land()

else:

    print("Battery too low.")

Below is an incorrect example. Try running it to see what happens. Your goal: correct the example by indenting correctly and fixing the syntax.

drones = 100

bugs = 55

if drones > bugs print("Squish the bugs!")

else print("Fly away!")

The example should look something like this. Try running it now and change the values of drones and bugs.

drones = 100

bugs = 55

if drones > bugs:

    print("Squish the bugs!")

else:

    print("Fly away!")

In the last few steps, you were introduced to a new symbol. The > sign is an example of a comparator, but you may know it as an inequality sign from math class. Comparators can be used inside conditions to compare values. If the statement is true, the statement below will execute. These are comparators:

• > Greater than
• < Less than
• >= Greater than or equal to
• <= Less than or equal to
• == Equal to
• != Not equal to

Here’s an example that uses them. Try it out for yourself! Run the code without changing the values, then change X and Y so that the sum is equal to 50. You can also try changing the comparator to see what happens!

import CoDrone_mini

from CoDrone_mini import Direction

drone = CoDrone_mini.CoDrone()

drone.pair()

X = 10

Y = 30

if X + Y == 50:

    print("Correct, X + Y is equal to 50.")

    drone.takeoff()

drone.flip(Direction.Forward)

drone.land()

else:

    print("Incorrect.")

Create 3 variables with different numerical values. Next, write at least 3 if statements and an else statement. Use the variables as the conditions for the if statements. The statements of the if statements and else statement should print different strings. The program below is an example — try writing your own!

import CoDrone_mini
drone = CoDrone_mini.CoDrone()
drone.pair()
 
x = 58
y = 12
z = 90
 
drone.takeoff()
if x > y:
   drone.set_pitch(50)
   drone.move(2)
if z > x:
   drone.set_roll(50)
   drone.move(2)
if y+z > x:
   drone.set_yaw(50)
   drone.move(2)
if y > z:
   drone.set_throttle(50)
   drone.move(2)
else:
   drone.land()

Pretend that you have two buttons: one button opens a door, and the other button closes the door. You also have code that will check if the buttons are pressed. Your first thought might be to write something like this:

if button 1 is pressed:

    Close the door

if button 2 is pressed:

    Open the door

What happens if you press both at the same time? Both are true and the door would try to open and close at the same time!

Else if statements, written as elif in Python, solve this problem. Once a condition is met, the code will not execute any of the other elif statements, whether they are true or not. Just like an if statement, if the code runs through all of the conditions and none are met, then the else statement will execute. Although you don’t need an else statement, it’s usually a good idea to include one to handle any errors or unexpected cases. Here is an adjusted code using elif.

if button 1 is pressed:

    Close the door

elif button 2 is pressed:

    Open the door

This challenge will be checking if a person is tall enough to ride a rollercoaster.

• You’ll declare a variable called  height , which will represent height in inches.
• The height should be checked at 48 and 36.
• Anyone under 36 inches is not allowed to ride.
• Riders between 36 and 48 inches can ride with a parent.
• Riders above 48 inches can ride alone.

Add the drone in by having it throttle up for 3 seconds at 48 inches and above and at 2 seconds for 36-48 inches. For any variable under 36 inches, it should yaw for 1 second.

import CoDrone_mini

drone = CoDrone_mini.CoDrone()

drone.pair()


height = 66  # height in inches

drone.takeoff()


if height > 48:

    drone.set_throttle(50)

    drone.move(3)

    print("Rider can ride alone")

elif height > 36:

    drone.set_throttle(50)

    drone.move(2)

    print("Rider must be accompanied by parent")

else:

    drone.set_yaw(50)

    drone.move(1)

    print("Rider not allowed on the ride")

drone.land()

drone.close()