3.1 if, elif, else Statements

3.1 if, elif, else Statements

Learning to make decisions in code with if, elif, and else structures, for creating conditional logic and executing different code blocks based on conditions.

The `if`, `elif` (which means "else if"), and `else` statements form the backbone of decision-making in programming. They allow you to execute different blocks of code depending on whether a specific condition is `True` or `False`.

The if Statement

It is the most basic control structure. The code block following the `if` will only be executed if the given condition is `True`. The syntax is: `if condition: # Code...`

The elif (else if) Statement

It is used when you want to check for multiple, mutually exclusive conditions. The code block following `elif` will be executed if the previous `if` (or `elif`) condition was `False` AND the current `elif` condition is `True`. You can have as many `elif` statements as you need.

The else Statement

It is optional and used as a "catch-all" case. The code block following `else` will be executed if all previous `if` and `elif` conditions were `False`.

"Truthy" and "Falsy" Values

In Python, conditions do not need to be strictly Boolean (`True`/`False`). Any value can be interpreted as "truthy" or "falsy". "Falsy" values are `None`, `False`, zero (`0`, `0.0`), empty collections (`""`, `[]`, `()`, `{}`), and empty sets. All other values are considered "truthy".

Nested if Statements

You can place an `if` statement inside another one. This is useful for more complex checks.

Ternary Operator

For simple `if-else` assignments in one line, you can use the ternary operator with the syntax: `value_if_true if condition else value_if_false`.
# Example 1: Simple if statement
temperature = 28
if temperature > 25:
    print("The temperature is high.")

print("-" * 30)

# Example 2: if-else
age = 19
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

print("-" * 30)

# Example 3: if-elif-else (Grade check)
grade = 75
if grade >= 90:
    print("Excellent!")
elif grade >= 70:
    print("Very good!")
elif grade >= 50:
    print("Good.")
else:
    print("You need to try harder.")

print("-" * 30)

# Example 4: Complex conditions with logical operators
is_user_logged_in = True
is_admin = False
if is_user_logged_in and is_admin:
    print("Access as administrator.")
elif is_user_logged_in and not is_admin:
    print("Access as a regular user.")
else:
    print("Please log in.")

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