Variables

Variables are important in all programming languages and in most programs! Just like in math, variables in programming are placeholders and data storage for numbers. Typically, you can create, or declare, a variable and save, or initialize, its value at the beginning of your program. You can then call that value later on in the program whenever you use the variable.

x = 2	        # Declaring variable x and initializing the value to 2
print(x)	# Calling the variable in a print statement

You can declare multiple variables to hold many values. Just be sure to give them different names, because a variable can change values when running a program. If you make a new variable with the same name as a previous one, the new value will override the old value.

x = 2	 # Declaring a variable x and initializing it to 2
print(x) # Printing initial value of x
x = 3	 # Reassigning variable x to 3
print(x) # Printing new value of x

Just like in your math class, you can do math with your variables. What do you think the following code will output? Try it out!

y = 4
z = 3
x = y + z
print(x)

This also works with subtraction, division, multiplication and other mathematical functions! In a future lesson, you will learn about exceptions when working with operations.

You can also assign variables to other types of data, like int, float, string,andboolean.

w = 4	                # this is an int
x = 3.2	                # this is a float
phrase = "Hello"	# this is a string
is_flying = True	# this is a boolean

• Int: a negative or positive whole number
• Float: decimal values
• String: a sequence of characters
• Boolean: can be set to True orFalse

If you are familiar with other programming languages, you may be wondering why we’re not including a data type in the initialization, such as:

# Warning! This is NOT proper Python syntax
int w = 4
float x = 3.2
String phrase = "Hello"
bool is_flying = True

In Python, variables can hold whatever type of value you want without needing to specify the type of data.

Create four variables: one integer, one decimal, one string, and one that’s your choice. Add print statements for each variable. Run the code!

Here’s an example:

x = 2
y = 25.3
z = 0.375
phrase = "message received"

print(x)
print(y)
print(z)
print(phrase)

Now that you know how to create variables, let’s use them in a program with CoDrone! Create a variable called durationand assign it to a value that will represent the number of seconds that you want the drone to perform an action. Next, call that variable inside functions in your program.

duration = 3.5	        # initialize variable 'duration' to 3.5

drone.takeoff()
drone.hover(duration)	# in this case, hover for 3.5 seconds
drone.set_pitch(50)	# Set positive pitch to 50% power
drone.move(duration)	# forward for 3.5 seconds
drone.land()
drone.close()

Change the value of duration to see how it affects the CoDrone. As duration increases, the CoDrone should hover and fly longer in the air.

duration = 5	        # initialize variable 'duration' to 5

drone.takeoff()
drone.hover(duration)	# in this case, hover for 5 seconds
drone.set_pitch(50)	# Set positive pitch to 50% power
drone.move(duration)	# forward for 5 seconds
drone.land()
drone.close()

Challenge: Variable square

Use the setup code provided to have your CoDrone take off and then fly in a square pattern! Note: this code will only have your drone take off, throttle up, and then land. You need to do the extra work to fly your CoDrone in a square!

Rules:

1. You are only allowed to use the existing variables, but you can change the
2. You can’t use any numbers aher you initialize the variables!

A = 1;
B = 500;
C = 5;
D = 2;
E = 10;
F = 3;

drone.takeoff()
drone.set_throttle((C * C) * F)	# 5 * 5 * 3	= 75; set throttle power t 75%
drone.move(A * D);	        # 1 * 2 = 2 ; move for 2 seconds
drone.land()drone.close()