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Lição 5. While cycle
Dificuldade:
Tarefa«Férias tão esperadas»
💻 Python
Anna sonha com férias e quer acumular um determinado valor para isso. Ela começa com um salário anual específico e planeja suas economias. A cada ano, seu empregador promete um aumento, e seu salário aumenta em 15% em relação ao ano anterior. Anna é muito disciplinada e decide economizar exatamente 10% de seu salário anual no final de cada ano.
Escreva um programa que ajude Anna a calcular quantos anos completos ela precisa para acumular o valor necessário. O programa deve perguntar ao usuário o salário anual atual de Anna e o custo das férias.
Condição adicional: após a exibição do resultado principal (o número de anos), o programa deve perguntar ao usuário se ele deseja ver um relatório detalhado por ano. Se o usuário digitar sim, o programa deve exibir para cada ano: o número do ano, o salário desse ano, quanto foi economizado e qual foi o valor total acumulado no final do ano.
Formato de entrada
Salário anual de Anna (número, float )
(Número, float )
A resposta para a pergunta de um relatório detalhado (string, str )
Formato de saída
Resultado principal: uma linha com informações sobre quantos anos serão necessários (linha, str )
Resultado adicional (opcionalmente): relatório detalhado para cada ano de economia (linhas, str )
Exemplo
Entrada
100000
50000
Sim
Saída
Anna levará 5 anos para economizar para as férias.
Deseja ver um relatório anual detalhado? (sim/não): & nbsp;
--- Relatório anual ---
ano 1: salário 100.000,00, foi reservado 10.000,00, total de 10.000,00
ano 2: salário 115.000,00, reservado 11.500,00, total acumulado 21.500,00
ano 3: salário 132.250,00, reservado 13.225,00, total acumulado 34.725,00
ano 4: salário 152.087,50, reservado 15.208,75, total acumulado 49.933,75
ano 5: salário 174.900,62, reservado 17.490,06, total acumulado 67.423,81
Dica
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 theindex < 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
breakstatement. Theelseblock is ignored in this case. - If the loop reaches the end (checked all the elements), it means that
breakhas never worked. Theindex < len(numbers)condition becomes false, and then theelseblock 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? Thecontinueoperator does not interrupt the loop, but only ends the current iteration ahead of schedule. It does not affect the execution of theelseblock in any way. - If the loop was never executed? If the
whilecondition is initially false, the loop body will not be executed even once. However, theelseblock will still run, since the loop ended "normally" (it was not interrupted viabreak).
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
forloops! The same logic applies tofor...elseloops. Theelseblock afterforis executed if the cycle has passed through all the elements and has not been interrupted usingbreak.
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
Teste 1
Teste 2
Teste 3
Teste 4
Teste 5
Teste 6
Teste 7
Teste 8
Teste 9
Teste 10
Solução do desenvolvedor
# Запрашиваем у пользователя начальные данные
initial_salary = float(input())
vacation_cost = float(input())
# Проверяем корректность введенных данных
if initial_salary <= 0 or vacation_cost <= 0:
print("Ошибка: Зарплата и стоимость отпуска должны быть положительными числами.")
else:
# Инициализация переменных для цикла
current_salary = initial_salary # Текущая годовая зарплата
total_savings = 0.0 # Общая сумма накоплений
years = 0 # Счетчик лет
# Список для хранения детальной информации по годам
yearly_details = []
# Цикл while работает, пока накопленная сумма меньше стоимости отпуска
while total_savings < vacation_cost:
years += 1 # Увеличиваем счетчик лет на 1
# Рассчитываем, сколько денег будет отложено в этом году (10%)
saved_this_year = current_salary * 0.10
# Добавляем отложенные деньги к общей сумме накоплений
total_savings += saved_this_year
# Сохраняем детали этого года для возможного отчета
yearly_details.append((years, current_salary, saved_this_year, total_savings))
# Увеличиваем зарплату на 15% для следующего года
current_salary *= 1.15
# Выводим основной результат
print(f"Анне потребуется {years} лет, чтобы накопить на отпуск.")
# Спрашиваем пользователя, нужен ли детальный отчет
show_details = input("Хотите увидеть подробный годовой отчет? (да/нет): ")
# Условие для вывода детального отчета
if show_details.lower() == 'да':
print("\n--- Годовой отчет ---")
# Цикл for для вывода информации по каждому году
for detail in yearly_details:
year, salary, saved, total = detail
# Выводим отформатированную строку с данными за год
print(f"Год {year}: Зарплата {salary:.2f}, Отложено {saved:.2f}, Всего накоплено {total:.2f}")
