理论与实践

数据输入输出

任务

条件语句

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for循环

任务

字符串

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while循环

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列表

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二维数组

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字典

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集合

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函数与递归

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课程 5. While cycle

难度：

任务«计算数字中的数字»

💻 Python

在他的古老实验室里，炼金术师阿利斯特发现了一种神奇的药剂。如果你把它滴在一张写有数字的羊皮纸上，药剂就会开始嘶嘶作响并发出光芒，随后空中会出现一个魔法符号，表示这个数字中的数字个数。阿利斯特不仅是一位炼金术师，还是一位新兴“技术魔法”（编程）的爱好者，他决定用代码重现这一效果。

你的任务——帮助阿利斯特编写一个魔法程序。这个咒语应接收一个数字作为输入，并判断其中包含多少个数字。

重要的魔法规则：

咒语应同时适用于正数和负数。
负数中的“负号”不计为数字。例如，数字 -123 中只有 3 个数字。
数字 0 由一位数字组成。

输入格式

输入到炼金术士设备中的是一个整数（integer）。

输出格式

输入数字（整数/整型）的位数。

示例

输入

-481516

输出

提示

While in python

In the Python programming language, the while loop construction can have an optional else block. This block is executed only when the loop completes in its natural way, that is, when its condition becomes false, and not as a result of a forced interruption using the break operator.

Syntax:

while condition:
    # the body of the loop
    # ...the code that runs on each iteration...
else:
    # else block
    # ...the code that is executed if the loop ended without a break...

You can think of the else block as a "plan B": it is triggered if the main goal within the loop (which is usually completed through a break) has not been achieved.

Usage example: Searching for an element

Consider a classic problem where we search for a number in a list. If a number is found, we immediately break the loop using break. If we have checked all the elements and still haven't found what we are looking for, the else block is executed.

numbers = [1, 2, 3, 4, 5]
target = 8 # Let's try to find a number that is not in the list.

index = 0
while index < len(numbers):
    if numbers[index] == target:
        print(f"Success! {target} found at {index}.")
break # Goal reached, exit the loop
    index += 1
else:
    # This block will be executed because break was not called
    print(f"The search is completed. {target} not found in the list.")

How it works:

The whileloop is executed as long as the index < len(numbers) condition is true.
Inside the loop, we check whether the current element is equal to the desired one (target).
If we find a value, a success message is displayed and the loop is immediately interrupted by the break statement. The else block is ignored in this case.
If the loop reaches the end (checked all the elements), it means that break has never worked. The index < len(numbers) condition becomes false, and then the else block is executed, reporting a failed search.

A useful tip: Using while...else helps to avoid "flagged" variables. Without this block, the code would look like this:

# Alternative version with "flag"
numbers = [1, 2, 3, 4, 5]
target = 8
found = False # Flag variable

index = 0
while index < len(numbers):
    if numbers[index] == target:
        found = True
        break
    index += 1

if found:
    print(f"Success! {target} found.")
else:
print(f"Search completed. {target} not found in the list.")

As you can see, the while...else construction makes the code cleaner, more concise, and more "Pythonic", eliminating the need to manually control the flag.

If `break` is missing

If there is no break operator in the body of the while loop, then the else block will always be executed after the loop ends.

count = 0
while count < 3:
print(f"Iteration number {count}")
count += 1
else:
print("The loop ended naturally, so the else block is executed.")

Here, the while loop runs until count is less than 3. As soon as count becomes 3, the loop condition becomes false, and control is transferred to the else block.

Important nuances

What about continue? The continue operator does not interrupt the loop, but only ends the current iteration ahead of schedule. It does not affect the execution of the else block in any way.
If the loop was never executed? If the while condition is initially false, the loop body will not be executed even once. However, the else block will still run, since the loop ended "normally" (it was not interrupted via break).

value = 10
while value < 5: # The condition is immediately false
    print("This text will never be printed")
else:
print("The cycle didn't even start, but it ended normally, so else worked.")

This also works for for loops! The same logic applies to for...else loops. The else block after for is executed if the cycle has passed through all the elements and has not been interrupted using break.

Output

The while...else construction is a powerful and elegant Python tool. It is ideal for situations where you need to perform an action only if the loop has completed its work completely without being interrupted. This is especially useful in search algorithms, condition checking, or when working with data streams, where break signals a special event, and else indicates a regular termination without any.

main.py

测试 1

测试 2

测试 3

测试 4

测试 5

测试 6

测试 7

测试 8

测试 9

测试 10

开发者解答

# Считываем входные данные от пользователя в виде строки
input_str = input()

# Преобразуем строку в целое число
number = int(input_str)

# Инициализируем счетчик цифр
digit_count = 0

# Проверяем особый случай: если число равно 0
if number == 0:
    # В числе 0 ровно одна цифра
    digit_count = 1
else:
    # Если число отрицательное, делаем его положительным для удобства подсчета
    if number < 0:
        number = -number  # Знак минуса не является цифрой

    # Запускаем цикл, который будет работать, пока в числе есть цифры
    while number > 0:
        # Целочисленно делим число на 10, отбрасывая последнюю цифру
        number = number // 10
        # Увеличиваем счетчик на 1 за каждую отброшенную цифру
        digit_count = digit_count + 1

# Выводим итоговое количество цифр
print(digit_count)