in the engineering company "exact mechanisms" engineers faced the necessary task: to synchronize the rotation of two new gears, they need to find their largest common divider (GCD). This will help determine the optimal number of teeth for intermediate gear shafts. To accelerate this process, the leadership asked you to create a program-calculator NOD.
54 24
NOD for numbers 54 and 24 is 6
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:
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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.
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:
whileloop is executed as long as the index < len(numbers) condition is true.target).break statement. The else block is ignored in this case.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.
break is missingIf 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.
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.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.")
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.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.
# Считываем два числа из одной строки и преобразуем их в целые числа
a, b = map(int, input().split())
a1 = a
b1 = b
# Реализация алгоритма Евклида с помощью цикла while
while b:
# В этой строке происходит "магия" алгоритма:
# a становится равным b, а b становится равным остатку от деления a на b.
# Это повторяется, пока b не станет равно 0.
a, b = b, a % b
# Когда цикл завершается, в переменной 'a' находится НОД.
print(f'НОД для чисел {a1} и {b1} равен {a}')1 - Read the task and understand what needs to be done
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