Chapter 2 Exercises

Practice exercises for loops and iteration in Python.

By Ali Berro

November 6, 2025 10 min read Section

From: Python Fundamentals: From Zero to Hero

python loops iteration exercises

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Section 19 of 61

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Exercises

Exercise 1: Countdown from n to 1

Write a program that reads a positive integer n from the user and prints a countdown from n to 1, each on a new line.

Answer:

1
n = int(input())
2
for i in range(n, 0, -1):
3
    print(i)

Exercise 2: Print characters at even positions

Write a program that reads a string from the user and prints all characters at even positions (indices 0, 2, 4, …), each on a new line.

Answer:

1
text = input()
2
for i in range(0, len(text), 2):
3
    print(text[i])

Exercise 3: Largest digit in a number

Write a program that reads a positive integer and finds and prints the largest digit in that number.

Answer:

1
num = int(input())
2
largest = 0
3
while num > 0:
4
    digit = num % 10
5
    if digit > largest:
6
        largest = digit
7
    num //= 10
8
print(largest)

Exercise 4: Sum of digits of a number

Write a program that reads a positive integer and calculates and prints the sum of all its digits.

Answer:

1
num = int(input())
2
sum_digits = 0
3
while num > 0:
4
    digit = num % 10
5
    sum_digits += digit
6
    num //= 10
7
print(sum_digits)

Exercise 5: Convert decimal to binary

Write a program that reads a positive integer and converts it to binary representation (as a string) without using built-in conversion functions.

Answer:

1
n = int(input())
2
binary = ""
3
if n == 0:
4
    binary = "0"
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else:
6
  while n != 0:
7
    r = n % 2
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    binary = str(r) + binary
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    n = n // 2
10
print(binary)

Exercise 6: Sum of all factors of a number

Write a program that reads a positive integer n and calculates and prints the sum of all its factors (divisors).

Answer:

1
n = int(input())
2
sum_factors = 0
3
for i in range(1, n + 1):
4
    if n % i == 0:
5
        sum_factors += i
6
print(sum_factors)

Exercise 7: Check if number is palindrome

Write a program that reads a positive integer and checks if it is a palindrome (reads the same forwards and backwards). Print "Palindrome" if it is, otherwise print "Not Palindrome".

Answer:

1
num = int(input())
2
original = num
3
reversed_num = 0
4
while num > 0:
5
    digit = num % 10
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    reversed_num = reversed_num * 10 + digit
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    num //= 10
8
if original == reversed_num:
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    print("Palindrome")
10
else:
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    print("Not Palindrome")

Exercise 8: Calculate harmonic series

Write a program that reads a positive integer n and calculates the harmonic series $H_n = 1 + \frac{1}{2} + \frac{1}{3} + ... + \frac{1}{n}$ . Print the result rounded to 6 decimal places.

Answer:

1
n = int(input())
2
harmonic = 0.0
3
for i in range(1, n + 1):
4
    harmonic += 1.0 / i
5
print(round(harmonic, 6))

Exercise 9: Calculate Un series

Write a program that reads a positive integer n and calculates $U_n = \sum_{i=1}^{n} \frac{i^2}{i + 1}$ . Print the result rounded to 6 decimal places.

Answer:

1
n = int(input())
2
total = 0.0
3
for i in range(1, n + 1):
4
    total += (i * i) / (i + 1)
5
print(round(total, 6))

Exercise 10: Equilateral triangle pattern

Write a program that reads a positive integer n and prints an equilateral triangle pattern with n rows using asterisks.

Example: If n = 4, the output should be:

1
   *
2
  ***
3
 *****
4
*******

Answer:

1
n = int(input())
2
for i in range(1, n + 1):
3
    spaces = n - i
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    stars = 2 * i - 1
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    print(" " * spaces + "*" * stars)

Exercise 11: Diamond pattern

Write a program that reads a positive integer n and prints a diamond pattern with n rows in the upper half.

Example: If n = 4, the output should be:

1
   *
2
  ***
3
 *****
4
*******
5
 *****
6
  ***
7
   *

Answer:

1
n = int(input())
2
for i in range(1, n + 1):
3
    spaces = n - i
4
    stars = 2 * i - 1
5
    print(" " * spaces + "*" * stars)
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for i in range(n - 1, 0, -1):
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    spaces = n - i
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    stars = 2 * i - 1
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    print(" " * spaces + "*" * stars)

Exercise 12: FizzBuzz

Write a program that prints numbers from 1 to n (read from input), but:

For multiples of 3, print "Fizz" instead of the number
For multiples of 5, print "Buzz" instead of the number
For multiples of both 3 and 5, print "FizzBuzz" instead of the number
Otherwise, print the number

Each output should be on a new line.

Answer:

1
n = int(input())
2
for i in range(1, n + 1):
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    if i % 15 == 0:
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        print("FizzBuzz")
5
    elif i % 3 == 0:
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        print("Fizz")
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    elif i % 5 == 0:
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        print("Buzz")
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    else:
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        print(i)

Exercise 13: Find missing number

Write a program that reads an integer n, then reads n unique numbers (all between 0 and n inclusive, except one missing number). Find and print the missing number.

Example: If n = 5 and the numbers are 0, 1, 3, 4, 5, then 2 is missing.

Answer:

1
n = int(input())
2
total_sum = n * (n + 1) // 2
3
actual_sum = 0
4
for i in range(n):
5
    num = int(input())
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    actual_sum += num
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missing = total_sum - actual_sum
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print(missing)

Exercise 14: Approximate exponential function

Write a program that reads two numbers x and n, and approximates $e^x$ using the Taylor series expansion:

$1 + x + \frac{x^2}{2 \times 1} + \frac{x^3}{3 \times 2 \times 1} + ... + \frac{x^n}{factorial(n)}$

where factorial(n) is the product of all positive integers from 1 to n. Print the result rounded to 6 decimal places.

Answer:

1
x = float(input())
2
n = int(input())
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result = 1.0
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factorial = 1
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power = 1.0
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for i in range(1, n + 1):
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    factorial *= i
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    power *= x
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    result += power / factorial
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print(round(result, 6))

Exercise 15: Caesar cipher

Write a program that reads a string message and an integer n (shift position), then shifts each letter in the message by n positions in the alphabet. Only shift letters (a-z, A-Z), leave other characters unchanged. Assume wrapping around (z shifts to a, Z shifts to A).

Answer:

1
message = input()
2
n = int(input())
3
result = ""
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for char in message:
5
    if 'a' <= char <= 'z':
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        shifted = ord(char) + n
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        if shifted > ord('z'):
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            shifted -= 26
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        result += chr(shifted)
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    elif 'A' <= char <= 'Z':
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        shifted = ord(char) + n
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        if shifted > ord('Z'):
13
            shifted -= 26
14
        result += chr(shifted)
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    else:
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        result += char
17
print(result)

Course Progress

Section 19 of 61

Back to Course

Chapter 2 Exercises

Table of Contents

Table of Contents

Course Progress

Exercises

Exercise 1: Countdown from n to 1

Countdown

Exercise 2: Print characters at even positions

Even Position Characters

Exercise 3: Largest digit in a number

Largest Digit

Exercise 4: Sum of digits of a number

Sum of Digits

Exercise 5: Convert decimal to binary

Decimal to Binary

Exercise 6: Sum of all factors of a number

Sum of Factors

Exercise 7: Check if number is palindrome

Palindrome Check

Exercise 8: Calculate harmonic series

Harmonic Series

Exercise 9: Calculate Un series

Un Series

Exercise 10: Equilateral triangle pattern

Equilateral Triangle

Exercise 11: Diamond pattern

Diamond Pattern

Exercise 12: FizzBuzz

FizzBuzz

Exercise 13: Find missing number

Missing Number

Exercise 14: Approximate exponential function

Exponential Approximation

Exercise 15: Caesar cipher

Caesar Cipher

Course Progress