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Lektion 2. Conditions
Schwierigkeit:
Aufgabe«Virtueller Bauernhof»
💻 Python
Bauer Fjodor beschloss, seinen Bauernhof zu zählen und alle Tiere in drei neue geräumige Ställe zu bringen. Die Kapazität jedes Stalls — genau 10 Tiere.
rnSchreiben Sie ein Programm, das Fjodor hilft, schnell zu ermitteln, ob genug Platz für alle vorhanden ist. Das Programm soll den Bauern nach der Anzahl der Kühe, Schafe und Hühner fragen und dann mitteilen, ob sie in drei Ställen untergebracht werden können. Wenn Platz vorhanden ist, soll das Programm auch berechnen, wie viele freie Plätze übrig bleiben. Wenn nicht genug Platz vorhanden ist, muss angegeben werden, wie vielen Tieren der Platz fehlt.
Eingabeformat
Drei ganze Zahlen, jede wird nach der entsprechenden Aufforderung in einer neuen Zeile eingegeben.
Erste Zahl: die Anzahl der Kühe (ganze Zahl).
Zweite Zahl: die Anzahl der Schafe (ganze Zahl).
Dritte Zahl: die Anzahl der Hühner (ganze Zahl).
Ausgabeformat
Zwei Zeilen Text.
Erste Zeile: die Antwort auf die Frage, ob es möglich ist, Tiere unterzubringen (Zeile).
Zweite Zeile: die Anzahl der verbleibenden freien oder fehlenden Plätze (Zeile).
Beispiel
Eingabe
5
8
10
Ausgabe
Ja, alle Tiere können platziert werden.
Es werden freie Plätze geben: 7
Hinweis
Nested conditions
You can nest some conditional statements (if) into others to create more complex and multi-level checks. This is useful when the next action depends on several consecutive conditions.
The key point here is the correct indentation (usually 4 spaces), which shows Python which block of code belongs to which condition.
Example:
x = 10
if x > 5:
print("First check passed: x is greater than 5.")
if x < 20:
print("Second check passed: x is also less than 20.")
else:
print("Second check failed: x is at least 20.")
else:
print("First check failed: x is less than or equal to 5.")
A useful tip: Try not to create too many nesting levels (3 or more). Deeply embedded code becomes difficult to read and understand. Often, complex nesting can be simplified by using logical operators.
Logical operators
Logical operators in Python are used to combine two or more conditions. They allow you to build complex logic without putting conditions into each other. The main logical operators are and, or and not.
| The | Name | Description |
|---|---|---|
or |
logical "OR" | Returns True if at least one condition is true. |
and |
logical "And" | Returns True only if both conditions are true. |
not |
logical "NOT" (negation) | Inverts the result: True becomes False and vice versa. |
Examples:
a = 5
b = 7
# and: both conditions must be true
s1 = a > 3 and b < 10 # True and True -> True
# or: at least one condition must be true
s2 = a != 5 or b >= 7 # False or True -> True
# not: inverts the result
s3 = not (a < b) # not (True) -> False
When using and, the result will be true only if both operands are true. When using or, it is sufficient for at least one of the operands to be true. The not operator turns a lie into the truth and vice versa.
Analysis of a complex example:
a, b, c = 7, 10, 11
# Original expression:
print(not(a > 7 and b <= 10) or c != 17)
# Let's take it step by step:
# 1. a > 7 -> 7 > 7 -> False
# 2. b <= 10 -> 10 <= 10 -> True
# 3. (False and True) -> False
# 4. not(False) -> True
# 5. c != 17 -> 11 != 17 -> True
# 6. True or True -> True
# Result: True
A useful tip: To improve readability and avoid errors in complex expressions, always use parentheses () to explicitly specify the order of calculations, even if you remember the precedence of operators (not has the highest priority, then and, then or).
The ternary operator
The ternary operator is a compact way to write a simple if-else condition that returns a value. It allows you to assign a variable a value depending on the condition, and all this in one line.
Syntax: [value if true] if [condition] else [value if false]
Examples:
x = 10
# If x > 5, result will be 100, otherwise 200
result = 100 if x > 5 else 200
print(result) # Will output: 100
y = 20
# Assign the larger of the two values to the variable z
z = x if x > y else y
print(z) # Outputs: 20
# Assign a text value
result_text = "positive" if x > 0 else "non-positive"
print(result_text) # Outputs: positive
A useful tip: The ternary operator is great for simple assignments. However, if the logic becomes more complicated or if, depending on the condition, you need to perform different actions (rather than just return a value), it is better to use a full-fledged if-else construct to preserve the readability of the code.
One-line conditions
If the condition body (if, elif, or else) consists of only one instruction, Python allows you to write it in the same line after the colon.
Example:
x = 10
if x > 5: print("x is greater than 5")
Important style note: Although this notation is syntactically correct, it is often not recommended by the Python Code Style Guide (PEP 8). Placing instructions on a separate line with indentation improves readability and is a generally accepted standard. Use a one-line entry with care, mostly for very simple and obvious actions.
main.py
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Test 7
Test 8
Test 9
Test 10
Entwicklerlösung
# Запрашиваем у пользователя количество животных каждого вида.
# Функция int() преобразует введенный текст в целое число.
cows = int(input())
sheep = int(input())
chickens = int(input())
# Рассчитываем общее количество животных путем сложения.
total_animals = cows + sheep + chickens
# Определяем общую вместимость всех загонов (3 загона * 10 мест).
total_capacity = 30
# Используем условие if/else для проверки, поместятся ли все животные.
if total_animals <= total_capacity:
# Этот блок кода выполняется, если общее количество животных меньше или равно вместимости.
free_space = total_capacity - total_animals # Вычисляем количество свободных мест.
print("Да, всех животных можно разместить.")
print("Останется свободных мест:", free_space)
else:
# Этот блок кода выполняется, если животных больше, чем мест.
shortage = total_animals - total_capacity # Вычисляем, скольких мест не хватает.
print("Нет, всех животных разместить нельзя.")
print("Не хватает мест:", shortage)
