Conditionals

Conditionals allow your program to make decisions based on certain conditions. They enable you to execute specific blocks of code depending on whether a condition evaluates to True or False.

The if Statement

The if statement is the simplest conditional. If the condition evaluates to True, the code block inside it runs.

Syntax:

if condition:
    # Code to execute if condition is True

Example:

age = 18

if age >= 18:
    print("You are eligible to vote.")

The if-else Statement

Use if-else to specify an alternative block of code to run if the condition is False.

Syntax:

if condition:
    # Code to execute if condition is True
else:
    # Code to execute if condition is False

Example:

age = 16

if age >= 18:
    print("You are eligible to vote.")
else:
    print("You are not eligible to vote.")

The if-elif-else Statement

When you have multiple conditions, use elif (short for “else if”). The else block is optional and executes if none of the conditions are True.

Syntax:

if condition1:
    # Code for condition1
elif condition2:
    # Code for condition2
else:
    # Code if no conditions are True

Example:

grade = 85

if grade >= 90:
    print("Grade: A")
elif grade >= 80:
    print("Grade: B")
elif grade >= 70:
    print("Grade: C")
else:
    print("Grade: F")

Nested Conditionals

Conditionals can be nested inside other conditionals for more complex logic.

Example:

age = 20
citizen = True

if age >= 18:
    if citizen:
        print("You are eligible to vote.")
    else:
        print("You must be a citizen to vote.")
else:
    print("You are not old enough to vote.")

Conditional Expressions (Ternary Operator)

Python supports a shorthand way of writing conditionals using a single line.

Syntax:

value = true_value if condition else false_value

Example:

age = 18
status = "Adult" if age >= 18 else "Minor"
print(status)  # Adult

Common Pitfalls

1. Indentation Errors: Always use consistent indentation for the code blocks inside conditionals.

   if True:
   print("This will cause an error!")  # IndentationError
   

2. Logical Mistakes: Ensure your conditions are logically correct to avoid unexpected results.

Practice Exercises

1. Write a program that:
   • Asks the user for a number.
   • Prints whether the number is even or odd.
2. Create a program to:
   • Ask the user for their age.
   • Print one of the following:
     • “Child” if age < 13.
     • “Teenager” if 13 ≤ age < 20.
     • “Adult” if age ≥ 20.
3. Build a simple calculator:
   • Ask the user for two numbers and an operation (+, -, *, /).
   • Perform the operation and print the result. Handle invalid operators gracefully.

Conditionals are a powerful tool for making your programs dynamic and responsive to user input!