Variables and Basic Operators

What are Variables?

A variable is like a container that holds data. It gives data a name, so you can refer to it later.

For example:

age = 25
name = "John"

Here:

• age is a variable storing the number 25.
• name is a variable storing the string "John".

#Exercise: Do you remember the print function from the previous session?
#Create a variable with your name and print your name to the console using print

Naming Rules for Variables?

Here are the rules for naming variables in Python:

• Variable names can only contain letters (a-z, A-Z), numbers (0-9), and underscores (_).
• Variable names cannot start with a number.
• Variable names are case-sensitive (Name and name are different).
• You cannot use Python keywords (like if, for, while) as variable names.

Valid examples:

my_age = 20
total_score = 99

Invalid examples:

1st_place = "Gold"  # Cannot start with a number
for = 10            # 'for' is a Python keyword

#Please fix these variable names so that the program runs without any errors.
#Explain why these are not valid variable names.
#Assign them a value using assignment operator = and print the values using the print function
1variable
3cats
0_value

variable-nam
my@var
data%size

my variable
user name

if
for
class
True
False

Assigning Values to Variables

You can assign values to variables using the = operator:

x = 5
y = 10
name = "Alice"

You can also update the value of a variable:

x = 5
x = x + 10  # Now x is 15

Assign multiple variables in one line

x, y, z = 5, 10, 15

Exercise: Favorite Things.

• Objective: Using print function display your name, favorite color, lucky number, and hobby.

#Hint: print function was discussed in previous session.
print("PAwan")
print("Red")
print("2")
print("reading")

• Objective: Create variables for your name, favorite color, lucky number, and hobby. Using print function print the values of these variables.

my_name = "Pawan"
fav_color = "Red"
lucky_number = "2"
hobby = "reading"
print(my_name)
print(fav_color)
print(lucky_number)
print(hobby)

# Create four variables: my_name, favorite_color, lucky_number, and favorite_hobby.

• Objective: Reassign the above variables with name, favorite color, lucky number, and hobby of the person next to you and print the same.

# Use the above variables and reassign the values
my_name = "Pawan"
fav_color = "Red"
lucky_number = "2"
hobby = "reading"
print(my_name)
print(fav_color)
print(lucky_number)
print(hobby)
my_name = "Aditya"
fav_color = "Blue"
lucky_number = "5"
hobby = "guitar"
print(my_name)
print(fav_color)
print(lucky_number)
print(hobby)

##Basic Operators

Python supports many operators to perform calculations and operations on variables.

###Arithmetic Operators

Operator	Description	Example
+	Addition	x + y
-	Subtraction	x - y
*	Multiplication	x * y
/	Division	x / y
**	Exponentiation	x ** y (x to the power of y)
%	Modulus (Remainder)	x % y

Example:

a = 10
b = 3
print(a + b)  # 13
print(a - b)  # 7
print(a * b)  # 30
print(a / b)  # 3.3333...
print(a % b)  # 1
print(a ** b) # 1000

Exercise: Basic Math Operations

• Objective: Reassign the number in following code snippet by adding, subtracting, multiplying, and dividing 5. Print the outout after each operation.

number = 10
#Add your code after this line

• Objective: Using basic math operators finish the following exercises.

a, b, c = 5, 7, 9
#Using the above variables print 12
#Using the above variables print 2
#Using the above variables print 0
#Using the above variables print 35

Exercise: Temperature Conversion.

Celsius (°C) and Fahrenheit (°F) are two scales used to measure temperature. They are commonly used in different parts of the world, and understanding their differences can help in various scientific and practical applications.

-Objective: What is the temperature outside? Is it in celsius or fahrenheit? If it is in celcius convert it in fahrenheit

The formula to convert Celsius to Fahrenheit is:

F = (C × 9 / 5 ) + 32

• Objective: Can you think of a country where temperature is measured in Fahrenheit (°F)? Find a city from that country and get its current temperature.

Convert that temperature to Celcius using formula:

C = (F − 32) × 5 / 9

###Comparison Operators These are used to compare two values and return True or False.

Operator	Description	Example
==	Equal to	x == y
!=	Not equal to	x != y
>	Greater than	x > y
<	Less than	x < y
>=	Greater than or equal to	x >= y
<=	Less than or equal to	x <= y

a = 10
b = 5
print(a == b)  # False
print(a > b)   # True

###Logical Operators Used to combine multiple conditions:

• and (True if both conditions are true)
• or (True if at least one condition is true)
• not (Reverses the condition)

Example:

x = 10
print(x > 5 and x < 15)  # True
print(x > 5 or x < 5)    # True
print(not (x > 5))       # False