Variables and Variable Declarations

Variables are how our programs are going to remember information. Our variables have two parts: names and values. When we create a variable we set its name and assign it an initial value.

name = value

The name always goes on the left of the equals sign and the value always goes on the right of the equals sign. If you switch these you will get an error!

For example, if I want a variable called age to have the value 91, I would write:

age = 91

We can use any name for our variables as long as they begin with a letter. Ideally, we want names that are descriptive of the values that the variables hold.

my_var = 1
a = 2

# notice that we separate words with
# underscores to improve readability!
flying_purple_people_eater = 3 

secrets = 42

Once we’ve declared a variable, we can then use its value later in our program. For instance, if I want to print out the value of a variable, I need to pass the variable as the argument of the print function:

print(variable)

So for our example with the variable age, a completed example would have the code:

age = 91 # declare the variable first
print(age) # now I can print it out

age = 91 # declare the variable first
print(age) # now I can print it out

# TODO: run this code. Does the print function print the name of the 
# variable or its value?
# Answer: 

a = 7
# TODO: write a line of code that prints 
# the value of the variable a

# TODO: write a line of code that declares
# a new variable and sets its value equal to 999

We can also do math with variables!

Remember, we always have the variable name on the left and its value on the right.

For instance:

my_big_number = 100000 + 547362
my_small_number = -799 - 47

If we want to use a variable in a calculation, that’s also okay:

first_num = 54
second_num = first_num + 72
print(second_num)

Remember: variables must always be declared before you use them!

We’ll explore what kinds of math operations we can use with variables when we talk about data types.

x = 10
y = -1
# TODO: write the code that creates a new variable and sets its 
# value equal to the sum of x and y. Then, print out the value of 
# that variable. Can you print out the sum of x and y without saving 
# the value in a variable first?