in the world where time flows in the opposite direction, the famous researcher, Dr. Elara Wence, conducts an experiment with his time machine. She launches the car from the initial “temporary coordinates” & nbsp; n & nbsp; and the machine starts the countdown to the & nbsp; 1 , which is the reference point (our present).
rnthe on-board computer of the car must record each temporary coordinate through which the car passes. However, for key points of travel, he should make special notes:
rn
EN
RU
EN
RU
": the beginning of the reverse trip!" ": arrival at the reference point!" rn your task & mdash; Write a program that emulates the work of the on -board journal of the time of Dr. Vance. The program receives an initial coordinate & nbsp; n & nbsp; and displays a full journal of travel.
rnClarification: If the middle of the track coincides with the final point (for example, for n = 2 or n = 3), priority has a message about arrival at the reference point.
10
10: Start of a return trip!
9
8
7
6
5: Half The paths are traveled!
4
3
2
1: Arrival to the reference point!
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.# Получаем начальную временную координату от пользователя
n = int(input())
# Рассчитываем координату середины пути с помощью целочисленного деления
midpoint = n // 2
# Запускаем цикл, который будет идти от n до 1 включительно, с шагом -1
for i in range(n, 0, -1):
# Проверяем, является ли текущая координата начальной точкой
if i == n:
print(f"{i}: Начало обратного путешествия!")
# Если нет, проверяем, является ли она конечной точкой
elif i == 1:
print(f"{i}: Прибытие в точку отсчета!")
# Если нет, проверяем, является ли она серединой пути
elif i == midpoint:
print(f"{i}: Половина пути пройдена!")
# Если это ни одна из ключевых точек, просто выводим координату
else:
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