INTRO   O

PROBLEM SOLVING AND

PROGRAMMING IN PYTHON

 

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Prof. Andrea Gallegati
tuj81353@temple.edu

Prof. Dario Abbondanza
tuk96119@temple.edu

CIS 1051 - IF STATEMENT

Understanding the

statement

 MAKING Decisions in Code

if

Every day, we make decisions based on conditions:


    • If it’s sunny, we wear sunglasses.
    • If we’re hungry, we eat.
    • If our phone battery is low, we charge it.

    Syntax:

    write Python programs that react to different conditions

    if condition:
	# Code that runs if 
	# the condition is True
	pass

    it allows us to execute a block of code only when a
    specific condition is met    .

    • An expression that evaluates to True or False.
    • A colon (:) fends the header.
    • The indented block below is the body.

    Example: Checking the Weather

    import random

# Define different weather conditions
w_conditions = ["rainy", "sunny", "cloudy"]

# Pick a random value from the above list
weather = random.choice(w_conditions)

# Print the random value
print("The weather is " + weather + ".")

if weather == "rainy":
    print("Don't forget your umbrella!")

    Using  <!=>

    Comparison Operators

    Operator Meaning Example (x = 10, y = 5)
    > Greater than x > y → True
    < Less than x < y → False
    >= Greater than or equal to x >= 10 → True
    <= Less than or equal to y <= 5 → True
    == Equal to x == y → False
    != Not equal to x != y → True

    in Conditions

    Example: Grading Exams

    import random

# Define the list of scores
grades = [20, 45, 56, 68, 75, 100]

# Pick a random value from the list
score = random.choice(grades)

# Print the random score
print("Score: " + str(score))

if score >= 60:
    print("Congratulations!")
    print(" You passed the exam.")

    The else Statement

    an alternative 

    import random

# Define the range of possible scores
min_score = 20
max_score = 100

# Pick a random score
score = random.randint(min_score, 
                       max_score)

# Print the random score
print("Score: " + str(score))

# Check if score meets the condition
if score >= 60:
    message_1 = "Congratulations! "
    message_2 = "You passed the exam."

else:
    message_1 = "Sorry, you didn't pass."
    message_2 = " Try Again!"

print(message_1 + message_2)

    The elif Statement

    multiple conditions

    import random

# Define the range of possible scores
min_score = 20
max_score = 100

# Pick a random score
score = random.randint(min_score, 
                       max_score)

# Print the random score and
# the corresponding Grade

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

    What Happens?

    • If score >= 90, it prints "Grade: A".
    • Otherwise, it checks if score >= 80... and so forth!

     

    The program stops checking after the first True condition.

    Operator Meaning Example (x = 8, y = 5)
    and Both conditions must
    be True     		x > 5 and y > 2 
    → True
    or At least one condition
    is True     		x > 10 or y < 10 
    → True
    not Negates the condition not (x > 10) → True

    Logical operators

    Age Verification for Discount 

    age = 17
is_student = True

if age < 18 and is_student:
    print("You get a student discount!")

    Checking for Even Numbers

    number = 7

if number % 2 == 0:
    print(str(number) + " is even.")
else:
    print(str(number) + " is odd.")

    NESTED if Statements

    age = 20
citizenship = "US"

if age >= 18:
    if citizenship == "US":
        print("You are eligible to vote.")
    else:
        print("You must be a US citizen to vote.")
else:
    print("You must be at least 18 to vote.")

    How It Works

    1. Checks if age >= 18 is True.
    2. Checks if the person is a US citizen is True.
    3. If both are True, it prints "You are eligible to vote."
      Otherwise, it prints "You must be a US citizen."
    4. If age < 18, it prints "You must be at least 18 to vote."

    Recap

    • if statement executes a code block (condition True).
    • else statement provides an alternative action.
    • elif statement allows multiple conditions.
       
    • Comparison operators (==, !=, >, <, >=, <=) 
      help define conditions.
    • Logical operators (and, or, not) 
      combine multiple conditions.
       
    • Nested if statements allow deeper decision-making.

    Try It Yourself!

    write a Python program that checks the temperature and prints different messages 

    temperature = 15  # Try changing this value!

if temperature > 30:
    print("It's hot outside! Stay hydrated.")
elif temperature > 20:
    print("The weather is nice and warm.")
elif temperature > 10:
    print("It's a bit chilly, grab a sweater.")
else:
    print("Brrr! It's freezing outside!")

    Great Work! 🎉

    Now you understand if statements and conditional logic in Python!


    Ready to try them out? 🚀

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    By Andrea Gallegati

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