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 Else, I will stay asleep.
2. If I am hungry, I will eat
3. If it’s sunny out, I will wear
4. If my room is clean, I will get my Else, I will make no money.

If statements are written like this:

if insert condition here:
    Insert statements here
else:
    Insert statements here

# Example below

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. What if you want to have multiple statements execute if a condition is true? If you use proper indentation, it would look like this:

if (drone.connected()):
    print("Drone is connected!")
    CoDrone.takeoff()
    CoDrone.land()
else:
    print("Not paired")

Below is an incorrect example. Try running it in PyCharm to see what happens. Your goal: correct the example by indenting correctly!

drones = 100
bugs = 55
if drones > bugs:
print("Squish the bugs!")
if drones + bugs > 90:
print("Run away!")

The example should look something like this. Try running it now!

drones = 100
bugs = 55
if drones > bugs:
    print("Squish the bugs!")
if drones + bugs > 90:
    print("Run away!")

In the last step, 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!

X = 10
Y = 100
if (X != Y):
    print("Correct, X is not equal to Y")
    Z=100
if (Z == Y):
    print("Correct, Z is equal to Y")

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!

x = 58
y = 12
z = 90
if x > y:
   print("jelly")
if z > x:
   print("peanut butter")
if y+z > x:
   print("bread")
if y > z:
   print("toast")
else :
   print("best sandwich ever")

Nested if statements are if statements inside another if statement. Check the code below for a real-life example, and then look at the flowchart in the first picture for an even better understanding.

if it is sunny outside:
    if it is hot:
        I will go swimming
    else:			#it is NOT hot
        I will play baseball
else:				#it is NOT sunny
    I will play inside

Nested if statements are useful in situations like having multiple conditions for the same purpose, or for follow-up questions. The programs below are other examples.

if you are happy:
    keep doing whatever you’re doing
else:
    if you do want to be happy:
        change something
    else:
        keep doing whatever you’re doing

Make three variables and use them for the conditions of two if statements. The if statements should be nested. Each if statement should print a string. The combined string should complete a phrase. A separate if statement that prints a different string should follow the nested if statement. The program below is an example — try writing your own!

x = 3
y = 6
z = 9
if x < y:
    print("I love to")
    if y < z:
        print("program!")
if z > x:
    print("What do you love?")

Below is an incorrect example. Your goal is to debug it so it runs without any errors.

Test = 75.50
A = 90
B = 80
C = 70
D = 60
F = 50
if Test == 100:
print("Automatic pass!")
if Test > A:
print("Student receives an A")
else:
if Test > B:
print("Student receives a B")
else:
if Test > C:
print("Student receives a C")
else:
if Test > D:
print("Student receives a D, please seek tutoring")
else:
if Test > F:
print("Student has failed, please seek tutoring")

Which string should be printed? Run the code to see if you’re correct!

Correct Answer:

Test = 75.50
A = 90
B = 80
C = 70
D = 60
F = 50
if Test == 100:
    print("Automatic pass!")
if Test > A:
    print("Student receives an A")
else:
    if Test > B:
        print("Student receives a B")
else:
    if Test > C:
        print("Student receives a C")
    else:
        if Test > D:
            print("Student receives a D, please seek tutoring")
        else:
            if Test > F:
                print("Student has failed	please seek tutoring")

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 elifin Python, solve this problem. Once a condition is met, the code will not execute any of the other elifstatements, 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’s an example that shows why you should use else-if statements. Imagine that you want to go see a movie and you need to buy tickets. The movie theatre has different ticket prices depending on your age. Children less than 5 years old pay nothing for their ticket. However, if you are a child less than 18 years old then you pay $8. If you are younger than 55 then you pay $12. Else, you pay a discounted price of $10.

if age < 5:
    price = 0
elif age < 18:
    price = 8
elif age < 55:
    price = 12
else:
    price = 10

Now suppose you used if statements for all of the cases and you entered that you are 15 years old. The first statement would not run, but statements two and three would both be true because fifteen is less than both 18 and 55. Since the computer reads statements in order, the price would hold the most recent value, which is $12. You would be overcharged for a movie! With elif statements, the code would have found the second condition to be true and ignored the rest of the conditions.

Try this out by adding print statements to the code above!

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 60 and 48. Anyone under 48 inches is not allowed to ride. Riders above 48 and below can ride with a parent. Riders above 60 inches can ride alone.

INSTRUCTOR TIP:

height = 66	# height in inches
if height > 48:
    print("Rider can ride alone")
elif height > 36:
    print("Rider must be accompanied by parent")
else:
    print("Rider not allowed on the ride")

In case you’re not entirely sure what a Magic 8 Ball is, it’s a toy that predicts your future when you ask it yes or no questions. Responses can be positive, negative, or unsure.

You will need to program your CoDrone to operate like a Magic 8 Ball! Have a variable where you can type a number from at least 1 to 6 in, and then program your drone to print an answer and fly in a certain direction for each response. We got part of it started for you — you just need to do the rest!

Rules:

• You must use one if statement, one else statement, and as many else if statements as you need in between.
• Include a space for a user to type a number with the Magic 8 Ball variable.
• You must have at least 6 responses – 2 negative, 2 positive, and 2 unsure.

import CoDrone

ball =	#user picks a number

drone = CoDrone.CoDrone()
drone.pair(drone.Nearest)

drone.takeoff()
if ball == 1:
    print('It is certain')
    drone.set_pitch(50)
    drone.move(2)
    
drone.land()	# lands the CoDrone
drone.close()