Python- Day 16-IF Statements

Once you understand conditional tests, you can start using if statements to control the flow of your Python programs.

There are different types of if statements and the one you choose depends on how many conditions you want to check.

Simple if Statements:

A simple if statement tests one condition and performs an action based on the result:

if conditional_test:
    # Do something

The condition is evaluated as either True or False.
If it's True, the code inside the indented block is executed. Otherwise, Python skips that block.

For example, you can check if a person is old enough to vote:

age = 19
if age >= 18:
    print("You are old enough to vote!")

This prints the message because the condition (age >= 18) is True.

if-else Statements :

In many cases, you’ll want to take different actions depending on whether a condition passes or fails.

This is where an if-else structure is useful:

age = 17
if age >= 18:
    print("You are old enough to vote!")
else:
    print("Sorry, you are too young to vote.")

Here, if the condition (age >= 18) is False, Python will execute the else block instead, printing a different message.

if-elif-else Chain:

When you need to test multiple conditions, use an if-elif-else chain. Python evaluates each condition in order and executes the block of the first test that passes:

age = 12
if age < 4:
    print("Your admission cost is $0.")
elif age < 18:
    print("Your admission cost is $25.")
else:
    print("Your admission cost is $40.")

>>

Your admission cost is $25.

Here, the second test (age < 18) passes, so the message "Your admission cost is $25." is printed.

Multiple elif Blocks:

You can add more elif blocks to handle more complex conditions.

For example, if you want to add a senior discount:

age = 70
if age < 4:
    price = 0
elif age < 18:
    price = 25
elif age < 65:
    price = 40
else:
    price = 20

print(f"Your admission cost is ${price}.")

In this case, if the person is 65 or older, the price will be $20, as specified in the else block.

Omitting the else Block:

You don’t always need an else block.

If you have specific conditions to test, you can replace the else block with another elif statement:

age = 70
if age < 4:
    price = 0
elif age < 18:
    price = 25
elif age < 65:
    price = 40
elif age >= 65:
    price = 20

print(f"Your admission cost is ${price}.")

This approach ensures that every block of code is executed only when the correct condition is met, offering more control over the behavior of your program.

Testing Multiple Conditions:

Sometimes, you want to check multiple conditions independently.

In these cases, use multiple if statements without elif or else:

requested_toppings = ['mushrooms', 'extra cheese']

if 'mushrooms' in requested_toppings:
    print("Adding mushrooms.")
if 'pepperoni' in requested_toppings:
    print("Adding pepperoni.")
if 'extra cheese' in requested_toppings:
    print("Adding extra cheese.")

print("\nFinished making your pizza!")

In this example, Python checks each condition separately, so it adds both mushrooms and extra cheese to the pizza.

If you used an if-elif-else structure instead,
Python would stop checking after the first condition passes:

if 'mushrooms' in requested_toppings:
    print("Adding mushrooms.")
elif 'pepperoni' in requested_toppings:
    print("Adding pepperoni.")
elif 'extra cheese' in requested_toppings:
    print("Adding extra cheese.")

This code would only add mushrooms and skip the rest,
because Python stops checking after the first condition that is True.

Use a simple if statement when you need to test one condition.

Use if-else when you want one block of code to run if the condition passes, and a different block if it fails.

Use if-elif-else when you need to check multiple conditions.

Use multiple if statements when more than one condition needs to be checked and multiple actions may be required.

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