The Logic

1. Comparisons

Comparisons ask a question. The answer is always True or False.

10 == 10     # True
10 != 5      # True
10 > 5       # True
10 < 5       # False
10 >= 10     # True
10 <= 3      # False

Comparing variables

age = 22
print(age >= 18)     # True
print(age == 25)     # False

Comparing strings

name = "Ahmed"
print(name == "Ahmed")    # True
print(name == "ahmed")    # False

2. If / Elif / Else

Now you can make decisions based on that True or False.

If

age = 20
if age >= 18:
    print("Adult")

If / else

age = 14
if age >= 18:
    print("You can vote")
else:
    print("Too young")

If / elif / else

age = 14
if age < 12:
    price = 80
elif age < 18:
    price = 100
elif age < 65:
    price = 130
else:
    price = 90
print(f"Ticket: ${price}")

3. Logical Operators

Combine multiple conditions in one line.

and (both must be true)

age = 24
has_id = True
if age >= 18 and has_id:
    print("Entry allowed")

or (one must be true)

is_student = True
is_senior = False
if is_student or is_senior:
    print("Discount applied")

not (flips the value)

is_banned = False
if not is_banned:
    print("Welcome")

4. For Loops

You send "Eid Mubarak!" to 50 contacts. Without a loop, you type the message, hit send, type it again, hit send, 50 times. With a loop, you type it once and Python sends it to everyone on your list.

# Without a loop
print("Eid Mubarak, contact 1!")
print("Eid Mubarak, contact 2!")
print("Eid Mubarak, contact 3!")
# ... 47 more times

# With a loop
for i in range(1, 51):
    print(f"Eid Mubarak, contact {i}!")

Looping through a range

for i in range(5):
    print(i)       # 0, 1, 2, 3, 4

Range with start and stop

for i in range(1, 6):
    print(i)       # 1, 2, 3, 4, 5

Range with step

for i in range(0, 20, 5):
    print(i)       # 0, 5, 10, 15

Looping through a string

name = "Ahmed"
for letter in name:
    print(letter)

Loop with a condition

for i in range(1, 11):
    if i % 2 == 0:
        print(i)       # 2, 4, 6, 8, 10

Print only odd numbers

for i in range(1, 21):
    if i % 2 != 0:
        print(i)       # 1, 3, 5, 7 ... 19

5. While Loops

A for loop runs a set number of times. A while loop keeps running until a condition is no longer true.

Basic while loop

count = 1
while count <= 5:
    print(count)
    count += 1   # 1,2, 3, 4,5 

Adding until limit

total = 0
while total < 100:
    total = total + 25
    print(total)

Mental model: for = you know how many times. while = you don't know, just keep going until done.

Summary

Challenge 1: Can You Vote?

Ask the user for their age. If 18 or older, print "You can vote." If not, print how many years they have to wait.

Age: 15
You can't vote yet. 3 more years!

Challenge 2: Ticket Price

Ask the user for their age. Under 12: $5. 12-17: $8. 18+: $12. Print the price.

Age: 14
Ticket: $8

Challenge 3: Parking Fee

Ask the user how many hours they parked. 1 hour: $5, 2-3 hours: $10, 4+ hours: $20. Print the fee.

Hours: 4
Fee: $20

Challenge 4: Speed Check

Ask the user for the speed limit and their speed. If over the limit, the fine is $50 for every 10 km/h over. If not over, print "No fine."

Speed limit: 90
Your speed: 112
Over by: 22 km/h
Fine: $100

Challenge 5: Countdown

Ask the user for a number. Count down to 1 and print "Go!" at the end.

Start: 5
5
4
3
2
1
Go!

Challenge 6: Grade Checker

Ask the user for their score (0-100). Print the letter grade: A (90+), B (80-89), C (70-79), D (60-69), F (below 60).

Score: 85
Grade: B

Challenge 7: Even or Odd

Ask the user for a number. Print if it is even or odd. Then print all even numbers from 1 to that number.

Number: 10
10 is even

Even numbers: 2, 4, 6, 8, 10

Challenge 8: Discount Day

Ask for the day of the week and the price. Monday and Friday get 20% off. Wednesday gets 10% off. All other days full price.

Day: Monday
Price: $50
Discount: 20%
Final: $40

Challenge 9: Star Printer

Ask the user for a number. Print that many stars on one line.

Number: 7
*******

Challenge 10: Flight Check-in

Ask for passenger name, age, and bag weight. Must be 18+ to fly alone. Bag must be under 23 kg. If both pass, print boarding pass. If not, print which rule failed.

Name: Hodan
Age: 22
Bag weight: 18
========================
   BOARDING PASS
========================
Passenger: HODAN
Status: Checked in
========================