Python Basics

Python program to add two numbers

Description: Write a Python program that takes two numbers from the user and prints their sum.

Rules and hints:

• Use input() to read the numbers.
• input() gives a string, so convert it with int() (or float() for decimals).

Python program to add two numbers

num1 = int(input("Enter first number: "))
num2 = int(input("Enter second number: "))

total = num1 + num2
print("Sum =", total)

Output:

How it works

• The two input() calls read what the user types, as text.
• int() converts the text to a whole number. Without it, "12" + "8" would give 128.
• The sum is stored in total and printed.

Learn more in Python input() Function and Python Type Casting.

Python program to swap two variables

Description: Write a Python program to swap the values of two variables.

Rules and hints:

• Do it first with a third (temporary) variable.
• Then do it the Python way, in one line.

Python program to swap two variables

a = 10
b = 20
print("Before swap: a =", a, "b =", b)

a, b = b, a

print("After swap: a =", a, "b =", b)

Output:

How it works

• The line a, b = b, a builds a tuple (b, a) and unpacks it into a and b.
• In many other languages you need a third variable: temp = a, a = b, b = temp. That also works in Python.
• Swapping works with any type, not only numbers.

Python program to find the area of a circle

Description: Write a Python program to calculate the area of a circle when the radius is 5.

Rules and hints:

• Formula: area = pi x radius x radius.
• Use math.pi for the value of pi.
• Round the answer to 2 decimal places with round().

Python program for the area of a circle

import math

radius = 5
area = math.pi * radius ** 2

print("Area of the circle:", round(area, 2))

Output:

How it works

• radius ** 2 means radius to the power 2.
• math.pi is 3.141592653589793, so the exact area is 78.53981633974483.
• round(area, 2) keeps two digits after the decimal point.

See also Python Modules to learn about import.

Python program to convert Celsius to Fahrenheit

Description: Write a Python program to convert temperature from Celsius to Fahrenheit.

Rules and hints:

• Formula: Fahrenheit = Celsius x 9 / 5 + 32.
• Use an f-string to print the result.

Python program to convert Celsius to Fahrenheit

def to_fahrenheit(celsius):
    return celsius * 9 / 5 + 32

for c in (0, 100):
    f = to_fahrenheit(c)
    print(f"{c} C = {f} F")

Output:

How it works

• The function takes a Celsius value and returns the Fahrenheit value.
• The loop tests two famous values: water freezes at 0 C (32 F) and boils at 100 C (212 F).
• The / operator always returns a float, that is why we see 32.0.

Read What are f-strings? and Python Functions.