Conditional Statemants

Double Branch

if condition:
    statement
    # ...
else:
    statement
    # ...

Multiple Branches

if condition1:
    statement
elif condition2:
    statement
elif condition3:
    statement
else:
    statement

Examples

# Single branch
gpa_str = input("Enter your GPA:")
gpa = float(gpa_str)
if gpa > 3.5:
    print(f"GPA: {gpa}")

# Double branch
height_str = input("Enter height (cm):")
height = int(height_str)
if height >= 180:
    print("Above average height")
else:
    print("Below average height")

# Multiple branches
month_input = input("Enter month number (1-12):")
month = int(month_input)
if month == 1:
    print("January")
elif month == 2:
    print("February")
elif month == 3:
    print("March")
elif month == 4:
    print("April")
elif month == 5:
    print("May")
elif month == 6:
    print("June")
elif month == 7:
    print("July")
elif month == 8:
    print("August")
elif month == 9:
    print("September")
elif month == 10:
    print("October")
elif month == 11:
    print("November")
else:
    print("December")

While Loop

while condition:
    statement1
    statement2
    # ...

The loop terminates when the condition evaluates too False.

Example: Number Guesssing Game

import random

attempts = 0
user_wins = 0
system_wins = 0

while attempts < 5:
    print(f"Score - You:System is {user_wins} : {system_wins}")
    
    user_choice = int(input('Choose [0:Rock 1:Scissors 2:Paper]: '))
    system_choice = random.randint(0, 2)
    
    if user_choice == 0 and system_choice == 1:
        print("You scored!")
        attempts += 1
        user_wins += 1
    elif user_choice == 0 and system_choice == 2:
        print("System scored!")
        attempts += 1
        system_wins += 1
    elif user_choice == 1 and system_choice == 0:
        print("System scored!")
        attempts += 1
        system_wins += 1
    elif user_choice == 1 and system_choice == 2:
        print("You scored!")
        attempts += 1
        user_wins += 1
    elif user_choice == 2 and system_choice == 0:
        print("You scored!")
        attempts += 1
        user_wins += 1
    elif user_choice == 2 and system_choice == 1:
        print("System scored!")
        attempts += 1
        system_wins += 1
    else:
        print("Draw - no points awarded")

print(f"Final Score: {user_wins} : {system_wins}")

if user_wins > system_wins:
    print("Congratulations, you win!")
else:
    print("System wins this time!")

For Loop

Syntax

for element in iterable:
    statement
    # ...

The loop variable represents each item in the sequence. The loop iterates through all elements in the container.

Example

university = 'Zhejiang University of Technology'

for character in university:
    print(character)
    # pass serves as a placeholder when no operation is needed

The range() Function

The range() function generates a sequence of numbers:

range(start, stop, step)

• start: initial value (inclusive)
• stop: final value (exclusive, left-closed right-open interval)
• step: increment value

Practical Applications

# Print numbers 0-9
for i in range(10):
    print(i)

# Print even numbers from 0-10
for i in range(0, 11, 2):
    print(i)

# Print countdown from 10 to 1
for i in range(10, 0, -1):
    print(i)

Loop with Else Clause

Both for and while loops support an optional else block that executes when the loop completes normally (not interrupted by break).

# For-else example
numbers = [3, 7, 11, 14, 17]
target = 10

for num in numbers:
    if num == target:
        print(f"Found {target}")
        break
    print(f"Checking {num}")
else:
    print(f"{target} not found in the list")

# While-else example
counter = 0
while counter < 5:
    print(f"Iteration {counter}")
    counter += 1
else:
    print("Loop finished without break")

Nested Loops

Loops can be nested within other loops:

# Multiplication table
for i in range(1, 4):
    for j in range(1, 4):
        print(f"{i} x {j} = {i*j}")
    print("---")