Practice Lesson – The while Loop. Master basic sequences, sentinel values, complex conditions, and digit processing.

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Python Practice: The while Loop

Python Practice: The while Loop

Hands-on Exercises | From Basic Sequences to Digit Math

Part 1: Introduction to the while Loop

These exercises will help you understand how to generate sequences and control loop counters (incrementing and decrementing).

Task 1: Countdown
1.0 Point

Task: Write a program that reads n and prints all numbers from n down to 1 using a while loop.

📤 Example Output

Input: 5
Output: 5 4 3 2 1

Task 2: Sequence from 15 to 30
1.0 Point

Task: Output the sequence of integers from 15 to 30 inclusively: 15 16 17 ... 30. Use different variables for loop counters.

📤 Example Output

15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Task 3: Sequence with a Step
1.0 Point

Task: Output the sequence of integers: 3 5 7 9 ... 21 (from 3 to 21 with a step of 2).

📤 Example Output

3 5 7 9 11 13 15 17 19 21

Task 4: Descending Sequence
1.0 Point

Task: Output the sequence of integers: 20 18 16 ... 2 (from 20 down to 2 with a step of 2).

📤 Example Output

20 18 16 14 12 10 8 6 4 2

Task 5: Descending with Step and Sum
1.5 Points

Task: Output the sequence of integers: 15 12 9 6 3 0 (from 15 down to 0 with a step of 3). Calculate and print the sum of these integers.

📤 Example Output

15 12 9 6 3 0
Sum = 45

Task 6: Real Numbers Sequence
1.5 Points

Task: Output the sequence of real numbers: 0.1 0.3 0.5 0.7 0.9 1.1 using a while loop.

📤 Example Output

0.1 0.3 0.5 0.7 0.9 1.1

Part 2: Sentinel-Controlled Loops

In these tasks, the loop runs until a specific «stop» value (sentinel) is entered. Pay close attention to initialization and updating the input inside the loop.

Task 7: Sum until Zero
1.0 Point

Task: Write a program that reads integers from the user until 0 is entered, and then prints the sum of all the numbers entered (excluding the 0).

📤 Example Output

Input: 5
Input: 10
Input: 3
Input: 0
Output: 18

Task 8: Password Checker
1.0 Point

Task: Write a program that keeps asking the user for a password until they enter the correct password "python123". Print "Access Granted" when they enter it correctly.

📤 Example Output

Input: hello
Input: world
Input: python123
Output: Access Granted

Task 9: Average of Positive Numbers
1.5 Points

Task: Write a program that reads numbers until a negative number is entered. Calculate and print the average of all the positive numbers entered before the negative one. If no positive numbers were entered, print 0.

📤 Example Output

Input: 4
Input: 6
Input: 2
Input: -1
Output: Average: 4.0

Task 10: Reading Words until «stop»
1.5 Points

Task: Read words from the user one by one until the word "stop" is entered. Print the total number of words entered (not counting the word «stop»).

📤 Example Output

Input: Apple
Input: Banana
Input: Cherry
Input: stop
Output: 3

Part 3: The while Loop with Complex Conditions

These tasks require more advanced logical thinking and combining multiple mathematical operations inside the loop.

Task 11: Integers between A and B
1.5 Points

Task: Two integers A and B are given (A < B). Output integers between A and B (including A and B) in ascending order and output the total quantity of these numbers.

📤 Example Output

enter two numbers, please: A = 1, B = 7
1 2 3 4 5 6 7
quantity = 7

Task 12: Multiplication Table
1.5 Points

Task: Read an integer n. Using a while loop, print the multiplication table for n from 1 to 10 in the format n x i = result.

📤 Example Output

Input: 3
Output:
3 x 1 = 3
3 x 2 = 6
...
3 x 10 = 30

Task 13: Real Numbers Sequence and Product
2.0 Points

Task: Output the sequence of real numbers: 0.0 0.5 1.0 1.5 2.0 2.5. Calculate and print the product of these numbers.

📤 Example Output

0.0 0.5 1.0 1.5 2.0 2.5
Product = 0.0

Task 14: Smallest Power of 2
2.0 Points

Task: Read an integer N. Find the smallest power of 2 (i.e., \(2^k\)) that is strictly greater than N. Print the result.

📤 Example Output

Input: 10
Output: 16
(Explanation: 2^3 = 8, 2^4 = 16, so 16 is the smallest power of 2 greater than 10)

Part 4: Processing Digits – The Math

Use % 10 to extract the last digit and // 10 to remove it. Loop until the number becomes 0.

Task 15: Second Digit from the Right
1.0 Point

Task: Write a program that reads a natural number n (n > 9) and prints its second digit from the right.

📤 Example Output

Input: 4567
Output: 6

Input: 123
Output: 2

Task 16: Count of Even Digits
1.0 Point

Task: Write a program that reads a number and counts how many of its digits are even.

📤 Example Output

Input: 1234
Output: 2

Input: 1357
Output: 0

Task 17: Contains Digit
1.5 Points

Task: Write a program that reads a number and a digit, and checks if the digit exists in the number. Print YES or NO.

📤 Example Output

Input number: 4567
Input digit: 5
Output: YES

Task 18: Perfect Number Check (Simplified)
1.5 Points

Task: Write a program that reads a number and calculates the sum of its digits. If the sum is equal to the product of its digits, print "YES", otherwise print "NO". (E.g., 123: Sum=6, Product=6 -> YES).

📤 Example Output

Input: 123
Output: YES

Input: 456
Output: NO

Task 19: Maximum Digit
2.0 Points

Task: Read a natural number and find its maximum digit. Print the result.

📤 Example Output

Input: 53258
Output: 8

Task 20: Palindrome Check
2.0 Points

Task: Write a program that reads a number and determines if it is a palindrome (reads the same forwards and backwards). Compare the original number with its reverse.

📤 Example Output

Input: 121
Output: YES

Input: 123
Output: NO

Task 21: Sum of First and Last Digits
2.0 Points

Task: Read a natural number and calculate the sum of its first digit (leftmost) and its last digit (rightmost). Print the result.

📤 Example Output

Input: 5678
Output: 13
(Explanation: first digit = 5, last digit = 8, 5 + 8 = 13)

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