Learn Without Walls
📄 Save or print this lesson:
← Back to Module 5

Module 5 Practice Problems

15 problems to master loops in Python

Problem 1: Print 1 to 20

Easy

Use a for loop to print the numbers 1 through 20, each on its own line.

Use range(1, 21) since range does not include the stop value.

for i in range(1, 21):
    print(i)

Problem 2: Sum of Numbers

Easy

Ask the user for a number n. Calculate and print the sum of all integers from 1 to n.

Use an accumulator variable. Start with total = 0 and add each number in the range.

n = int(input("Enter a number: "))
total = 0

for i in range(1, n + 1):
    total += i

print(f"Sum of 1 to {n}: {total}")

Problem 3: Countdown

Easy

Ask the user for a starting number. Count down from that number to 1, then print "Liftoff!"

Use range(start, 0, -1) or a while loop that decrements.

start = int(input("Start countdown from: "))

for i in range(start, 0, -1):
    print(f"{i}...")

print("Liftoff!")

Problem 4: Even Numbers Only

Easy

Print all even numbers from 2 to 50 (inclusive) on a single line separated by spaces.

Use range(2, 51, 2) to step by 2.

for i in range(2, 51, 2):
    print(i, end=" ")

Problem 5: Character Counter

Easy

Ask the user for a string and a character. Count how many times that character appears in the string.

Loop through each character in the string. Use a counter variable.

text = input("Enter a string: ")
char = input("Enter a character to count: ")
count = 0

for letter in text:
    if letter == char:
        count += 1

print(f"'{char}' appears {count} time(s)")

Problem 6: Factorial

Medium

Ask for a number and calculate its factorial. For example, 5! = 5 × 4 × 3 × 2 × 1 = 120.

Start with result = 1 and multiply by each number from 1 to n.

n = int(input("Enter a number: "))
result = 1

for i in range(1, n + 1):
    result *= i

print(f"{n}! = {result}")

Problem 7: Guessing Game

Medium

Pick a secret number (hardcode it). Let the user guess repeatedly. After each guess, say "too high", "too low", or "correct!" Count the number of attempts.

Use a while loop that continues until the guess matches. Increment an attempts counter each loop.

secret = 42
attempts = 0

while True:
    guess = int(input("Guess the number (1-100): "))
    attempts += 1

    if guess < secret:
        print("Too low!")
    elif guess > secret:
        print("Too high!")
    else:
        print(f"Correct! You got it in {attempts} attempts.")
        break

Problem 8: Reverse a String

Medium

Ask the user for a string. Use a loop to build and print the reversed string (do not use slicing).

Start with an empty string reversed_str = "". Add each character to the front: reversed_str = char + reversed_str.

text = input("Enter a string: ")
reversed_str = ""

for char in text:
    reversed_str = char + reversed_str

print(f"Reversed: {reversed_str}")

Problem 9: FizzBuzz

Medium

Print numbers from 1 to 30. For multiples of 3, print "Fizz". For multiples of 5, print "Buzz". For multiples of both, print "FizzBuzz".

Check divisibility by both 3 and 5 first (using and), then by 3 alone, then by 5 alone.

for i in range(1, 31):
    if i % 3 == 0 and i % 5 == 0:
        print("FizzBuzz")
    elif i % 3 == 0:
        print("Fizz")
    elif i % 5 == 0:
        print("Buzz")
    else:
        print(i)

Problem 10: Input Validation

Medium

Keep asking the user for a test score (0-100) until they enter a valid number. Then print the score.

Use a while loop. Keep looping as long as the input is outside the valid range.

while True:
    score = int(input("Enter a score (0-100): "))
    if 0 <= score <= 100:
        break
    print("Invalid! Score must be between 0 and 100.")

print(f"Valid score entered: {score}")

Problem 11: Fibonacci Sequence

Hard

Print the first 15 Fibonacci numbers. The sequence starts with 0, 1, and each subsequent number is the sum of the previous two: 0, 1, 1, 2, 3, 5, 8, ...

Use two variables a = 0 and b = 1. Each iteration: print a, then update: a, b = b, a + b.

a = 0
b = 1

for i in range(15):
    print(a, end=" ")
    a, b = b, a + b
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

Problem 12: Star Rectangle

Hard

Ask the user for the number of rows and columns. Print a rectangle of stars using nested loops.

Outer loop for rows, inner loop for columns. Use print("*", end=" ") inside and print() after each row.

rows = int(input("Rows: "))
cols = int(input("Columns: "))

for i in range(rows):
    for j in range(cols):
        print("* ", end="")
    print()

Problem 13: Prime Numbers

Hard

Print all prime numbers between 2 and 50. A prime number is only divisible by 1 and itself.

For each number, check if it is divisible by any number from 2 to that number-1. If none divide evenly, it is prime. Use a flag variable or the for-else pattern.

for num in range(2, 51):
    is_prime = True
    for i in range(2, num):
        if num % i == 0:
            is_prime = False
            break
    if is_prime:
        print(num, end=" ")
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

Problem 14: Multiplication Table

Hard

Print a formatted multiplication table from 1 to 10. Align the numbers neatly in columns.

Use nested for loops. Format each number with f"{value:4}" for right-aligned 4-character width.

# Header row
print("   |", end="")
for i in range(1, 11):
    print(f"{i:4}", end="")
print()
print("---+" + "----" * 10)

# Table body
for i in range(1, 11):
    print(f"{i:2} |", end="")
    for j in range(1, 11):
        print(f"{i*j:4}", end="")
    print()

Problem 15: Diamond Pattern

Hard

Ask the user for a size n. Print a diamond pattern with 2n-1 rows. For example, n=3:

  *
 ***
*****
 ***
  *

Split it into two halves: top (including middle) and bottom. For the top: row i has (n-i-1) spaces and (2*i+1) stars. For the bottom: reverse the pattern.

n = int(input("Enter size: "))

# Top half (including middle)
for i in range(n):
    spaces = " " * (n - i - 1)
    stars = "*" * (2 * i + 1)
    print(spaces + stars)

# Bottom half
for i in range(n - 2, -1, -1):
    spaces = " " * (n - i - 1)
    stars = "*" * (2 * i + 1)
    print(spaces + stars)