you & mdash; Young apprentice in the laboratory of the great alchemist. Your mentor has opened a way to double the power of magical essences, which are represented by numerical meanings. However, his method works only with "pure" essences that have positive power. Essence with zero or negative power is considered unstable and cannot be transformed.
rnthe alchemist dictates to you the values of the essences for one after another. Your task & mdash; Create a program that will take these values until the alchemist says "stop". The program should process all the resulting essences: double the strength of each “clean” (positive) essence and bring the result to the screen. Unstable essences should simply be ignored.
rn task:
Write a program that:
The data sequence where each line contains either an integer (int) or the word "stop". The input ends after receiving the line "Stop".
The sequence of integers (int), each on a new line. These are double values of all positive numbers from the input sequence, derived in the same order.
10
-5
25
0
8
Stop
20
50
16
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HI
while loop in PythonThe while cycle (translated as "for now") allows you to repeat the execution of a block of code as long as a certain logical condition remains true (True). This is an indispensable tool when you don't know in advance exactly how many times you need to perform an action. The main difference from the for loop is that for is usually used to iterate over a known sequence (list, string, range), and while when the number of iterations depends on the fulfillment of some condition in during the program operation.
whileHere is the basic syntax of the while loop in Python:
while condition:
code block_
True or False. This can be not only a comparison of variables, but also, for example, checking the presence of items in the list or the value returned by the function. If the condition is true (True), the block_code is executed.whileLet's look at an example where we output numbers from 1 to 5:
count = 1
while count <= 5:
print(count)
count += 1 # The most important line: increase the value of the count variable by 1
Output:
1
2
3
4
5
Here we start with the value count = 1. Before each iteration, Python checks the condition count<=5. As long as it is true, a block of code is executed: the current value of count is printed, and then it increases by 1. As soon as count becomes 6, the condition 6 <= 5 becomes false (False), and the loop ends its work.
A useful tip: the variable that controls the loop (in our case count) is often called a counter or a loop control variable. It is extremely important to ensure that it changes within the loop in such a way that the condition sooner or later becomes false.
An infinite loop is a cycle that never ends. This happens when his condition always remains true.
count = 1
while count <= 5:
print(count)
# Error: we forgot to change the count value, so the condition will always be True.
To stop the execution of such a cycle, you need to interrupt the program manually (for example, by pressing Ctrl+C in the terminal).
However, it is worth noting that infinite loops are not always a mistake. Sometimes they are used intentionally, for example, in programs that need to run all the time: servers listening to connections, or game loops. In such cases, the while True construction is often used.:, and the exit from the loop is organized using a break for some special event.
break to exit the loop earlyWe can use the break operator to immediately and completely terminate the loop, even if its main condition is still true.
count = 1
while count <= 10: # The condition allows you to go up to 10
if count == 3:
print("We have met the number 3, we exit the loop.")
break # Exit the loop when count is 3
print(count)
count += 1
Output:
1
2
We have met the number 3, we exit the cycle.
A useful tip: if you have nested loops (one while inside the other), the break statement will interrupt execution of only the innermost loop in which it is located.
continue to skip an iterationThe continue operator skips the rest of the code in the current iteration and immediately proceeds to check the condition for the next iteration.
count = 0
while count < 5:
count += 1
if count == 3:
print("Skipping the number 3...")
continue # Skip the remaining code and move on to the next iteration
print(f"Processing the number: {count}")
Output:
Processing the number: 1
Processing the number: 2
Skip the number 3...
Process the number: 4
Processing the number: 5
It is important not to confuse continue with break. break stops the loop completely, and continue only completes the current step ahead of schedule.
while with user inputwhile loops are ideal for processing user input when data needs to be requested until it meets the required criteria.
import random
secret_number = random.randint(1, 10)
guess = None # Initialize the variable before the loop
# The loop will run until guess is equal to secret_number
while guess != secret_number:
guess_text = input("Guess a number from 1 to 10:")
# Check if the user has entered a number
if not guess_text.isdigit():
print("Please enter a number.")
continue # Skip the rest of the logic and request input again.
guess = int(guess_text)
if guess < secret_number:
print("Your number is less than the number you have guessed.")
elif guess> secret_number:
print("Your number is more than the number you have guessed.")
print(f"Congratulations! You guessed the number {secret_number}!")
while with block elseLoops in Python have an interesting and not the most well-known feature - the else block. The code in the else block is executed only if the loop ended naturally (that is, its condition became False), and was not interrupted by the break operator.
# Example where else will execute
count = 1
while count <= 3:
print(f"Iteration {count}")
count += 1
else:
print("The loop ended naturally.")
# Output:
# Iteration 1
# Iteration 2
# Iteration 3
# The cycle ended naturally.
# Example where else fails due to break
count = 1
while count <= 3:
if count == 2:
print("The loop is interrupted by the break statement.")
break
print(f"Iterate {count}")
count += 1
else:
print("This block will not be executed.")
# Output:
# Iteration 1
# The loop is interrupted by the break statement.
The while loop is a powerful tool in Python. Here are the main points to remember:
break and continue: Use break to exit the loop completely and continue to skip the current iteration.while True pattern: This is a convenient way to organize a cycle that must be interrupted by a complex internal condition using break.else block: Keep in mind that you can use the else block for code that should be executed only at the normal end of the loop.# Создаем пустой список, куда будем сохранять числовые значения эссенций.
essences = []
# Запускаем бесконечный цикл для ввода данных.
# Он будет прерван, когда пользователь введет "стоп".
while True:
# Считываем очередную строку, которую ввел пользователь.
user_input = input()
# Проверяем, не является ли введенная строка командой для остановки.
if user_input == "стоп":
# Если да, то выходим из цикла ввода.
break
# Если это не команда "стоп", значит, это число.
# Преобразуем строку в целое число и добавляем в наш список.
essences.append(int(user_input))
# Теперь проходим по всему списку собранных эссенций.
# Цикл for идеально подходит для перебора элементов списка.
for value in essences:
# Применяем правило алхимика: работаем только с чистыми (положительными) эссенциями.
if value > 0:
# Если значение положительное, умножаем его на 2 и выводим результат.
print(value * 2)1 - Read the task and understand what needs to be done
2 - The example shows how the input data will be provided and what output is expected
3 - Write the code considering the input, output, and the task itself.
1 - The “Run” button executes your code only on one set of input data, and you’ll see the result in the output window.
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To change the input data, click the “Run Test” button next to the input data you want to execute.
1 - Input Data is the window containing the values loaded into your program in place of input()
2 - Program Output is the window showing what your program prints. If it’s green, the output matches the expected result; if red, there are differences.
3 - Expected Output is the reference value used to verify the solution.
1 - Green means the program produced the correct output
2 - Red means the program’s output didn’t match the expected output for this data. The program output and the expected output must be identical, including spaces and punctuation!
If you see this banner, congratulations — everything is correct.
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You did an excellent job with the task! It was a challenging problem, but you found the correct solution. You are one step closer to mastering programming! Keep up the good work, because every stage you pass makes you even stronger.
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