Conditional Statements: Making Smart Decisions

Welcome to the decision-making world of programming! Just like in real life, your programs need to make choices based on different situations.

What are Conditional Statements?

Conditional statements are like traffic lights for your code:

Green light (if): Go ahead if condition is true
Yellow light (elif): Alternative path if first condition fails
Red light (else): Stop and do this if all else fails

The Basic if Statement

Real-Life Example: Coffee Shop Decision

hungry = True
has_money = True

if hungry:
    print("Let's get some food!")

if has_money:
    print("I can afford it!")

# Both conditions are checked independently

Code Example: Age Verification

age = 25

if age >= 18:
    print("You are eligible to vote!")
    print("You can also get a driver's license!")

print("Age check complete.")  # This always runs

if-else Statement

Real-Life Example: Weather Decision

is_raining = True

if is_raining:
    print("Take an umbrella!")
    print("Wear rain boots!")
else:
    print("Enjoy the sunshine!")
    print("Wear sunglasses!")

print("Ready for the day!")

Code Example: Pass/Fail System

score = 75
passing_score = 60

if score >= passing_score:
    print("Congratulations! You passed!")
    print(f"Your score: {score}/{passing_score}")
else:
    print("Sorry, you didn't pass.")
    print(f"You needed {passing_score}, but got {score}")
    print("Better luck next time!")

print("Exam evaluation complete.")

Multiple Conditions with elif

Real-Life Example: Movie Rating System

age = 16

if age >= 18:
    print("You can watch R-rated movies!")
elif age >= 13:
    print("You can watch PG-13 movies!")
elif age >= 10:
    print("You can watch PG movies!")
else:
    print("You can watch G-rated movies!")

print("Movie selection complete.")

Code Example: Grade Calculator

marks = 87

if marks >= 90:
    grade = "A"
    feedback = "Excellent work!"
elif marks >= 80:
    grade = "B"
    feedback = "Good job!"
elif marks >= 70:
    grade = "C"
    feedback = "Satisfactory"
elif marks >= 60:
    grade = "D"
    feedback = "Needs improvement"
else:
    grade = "F"
    feedback = "Try harder next time"

print(f"Your grade: {grade}")
print(f"Feedback: {feedback}")

Nested if Statements

Real-Life Example: Restaurant Decision

has_reservation = True
party_size = 6
is_vegetarian = False

if has_reservation:
    print("Welcome! You have a reservation.")
    if party_size <= 4:
        print("Table for 4 is ready.")
        if is_vegetarian:
            print("Would you like the vegetarian special?")
        else:
            print("Our chef recommends the steak tonight.")
    else:
        print("Large party - please wait 15 minutes.")
else:
    print("Sorry, we require reservations for parties over 2.")

username = "admin"
password = "secret123"
is_admin = True

if username == "admin":
    if password == "secret123":
        print("Login successful!")
        if is_admin:
            print("Welcome, Administrator!")
            print("You have full access.")
        else:
            print("Welcome, User!")
            print("You have limited access.")
    else:
        print("Incorrect password!")
else:
    print("Username not found!")

Comparison Operators

Basic Comparisons

x = 10
y = 20

# Equal to
if x == y:
    print("x equals y")

# Not equal to
if x != y:
    print("x is not equal to y")

# Greater than
if x > y:
    print("x is greater than y")

# Less than
if x < y:
    print("x is less than y")

# Greater than or equal to
if x >= y:
    print("x is greater than or equal to y")

# Less than or equal to
if x <= y:
    print("x is less than or equal to y")

String Comparisons

name = "Alice"

if name == "Alice":
    print("Hello, Alice!")

if name != "Bob":
    print("You're not Bob!")

# Case-sensitive comparison
if name.lower() == "alice":
    print("Hello, alice (case-insensitive)!")

Logical Operators

and Operator (Both conditions must be true)

age = 25
has_license = True

if age >= 18 and has_license:
    print("You can drive legally!")
else:
    print("You cannot drive legally.")

# Multiple conditions
temperature = 75
is_sunny = True
has_sunscreen = True

if temperature > 70 and is_sunny and has_sunscreen:
    print("Perfect day for the beach!")
else:
    print("Maybe stay indoors today.")

or Operator (At least one condition must be true)

is_weekend = False
is_holiday = True

if is_weekend or is_holiday:
    print("You can sleep in!")
else:
    print("Time to wake up for work!")

# Multiple conditions
has_cash = False
has_card = True
accepts_crypto = False

if has_cash or has_card or accepts_crypto:
    print("You can make the purchase!")
else:
    print("Payment method not accepted.")

not Operator (Reverses the condition)

is_raining = False

if not is_raining:
    print("No need for an umbrella!")
else:
    print("Don't forget your umbrella!")

# Combining with other operators
age = 15
has_permission = False

if not (age >= 18 or has_permission):
    print("Access denied - too young and no permission!")
else:
    print("Access granted!")

Complex Conditions

Real-Life Example: Job Application

age = 22
has_degree = True
has_experience = True
criminal_record = False

if (age >= 18 and age <= 65) and (has_degree or has_experience) and not criminal_record:
    print("Congratulations! You're eligible for the job.")
    if has_degree and has_experience:
        print("You meet all preferred qualifications!")
    elif has_degree or has_experience:
        print("You meet minimum qualifications.")
else:
    print("Sorry, you don't meet the requirements.")
    if age < 18:
        print("Reason: Too young")
    elif criminal_record:
        print("Reason: Background check failed")
    else:
        print("Reason: Missing qualifications")

Common Mistakes

1. Using = instead of ==

# ❌ Wrong - this assigns 5 to x, always True
x = 10
if x = 5:  # SyntaxError!
    print("This won't work")

# ✅ Correct - this compares x with 5
if x == 5:
    print("x equals 5")

2. Forgetting colons

# ❌ Wrong - missing colon
age = 20
if age >= 18
    print("Adult")  # IndentationError!

# ✅ Correct
if age >= 18:
    print("Adult")

3. Wrong indentation

# ❌ Wrong - inconsistent indentation
if age >= 18:
    print("You can vote!")
  print("This line is wrongly indented!")  # IndentationError!

# ✅ Correct
if age >= 18:
    print("You can vote!")
    print("This line is properly indented!")

Practice Exercises

Exercise 1: Number Classifier

Write a program that classifies a number as positive, negative, or zero.

Exercise 2: BMI Calculator

Create a BMI calculator that gives health recommendations based on BMI categories.

Exercise 3: Leap Year Checker

Write a program that determines if a year is a leap year.

Exercise 4: Ticket Price Calculator

Calculate movie ticket prices based on age and day of the week.

Exercise 5: Password Strength Checker

Create a simple password strength checker with multiple criteria.

Summary

Conditional statements help your program make decisions:

if: Execute code if condition is true
elif: Check alternative conditions
else: Execute code if no conditions are true
Comparison operators: ==, !=, <, >, <=, >=
Logical operators: and, or, not

Remember to:

Use == for comparison (not =)
Always use colons after conditions
Maintain consistent indentation
Test all branches of your conditions

Next: Loops - making your code repeat actions! 🔄

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