Master Loops & Conditions in Python

Flow Control Fundamentals

By default, Python executes code line by line from top to bottom. Flow control lets you change this behavior to make dynamic, intelligent programs.

Structure	Purpose	When to Use
`if/elif/else`	Make decisions	User input validation
`for item in collection`	Known iterations	Process lists, ranges
`while condition`	Unknown iterations	Games, user menus
`break/continue`	Control loop flow	Early exit, skip items

if/elif/else Statements

Basic Decision Making

age = 20

if age >= 18:
    print("You can vote!")           # Runs if TRUE
elif age >= 16:
    print("You can drive!")         # Runs if first FALSE
else:
    print("You're too young!")      # Runs if all FALSE
                

Multiple Conditions

score = 85

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
else:
    grade = "F"

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

Logical Operators

has_ticket = True
has_id = True
age = 21

if has_ticket and has_id and age >= 18:
    print("Entry granted!")  # All must be TRUE

if has_ticket or has_id:  # Either TRUE
    print("You have credentials")

if not has_id:  # Opposite
    print("Need ID")
                

for Loops - Known Iterations

Iterate Lists

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(f"I like {fruit}s")
# Output:
# I like apples
# I like bananas  
# I like cherries
                        

range() Function

# Numbers 0 to 4
for i in range(5):
    print(i)

# Numbers 1 to 5
for i in range(1, 6):
    print(i)

# Step by 2
for i in range(0, 10, 2):
    print(i)  # 0, 2, 4, 6, 8
                        

enumerate() - Index + Value

students = ["Alice", "Bob", "Charlie"]
for index, name in enumerate(students):
    print(f"{index + 1}: {name}")
# 1: Alice
# 2: Bob  
# 3: Charlie
                

while Loops - Unknown Iterations

Counting Loop

count = 0
while count < 5:
    print(f"Count: {count}")
    count += 1  # Don't forget this!
# Output: 0, 1, 2, 3, 4
                

Guessing Game

secret = 7
guess = 0

while guess != secret:
    guess = int(input("Guess the number (1-10): "))
    if guess < secret:
        print("Too low!")
    elif guess > secret:
        print("Too high!")
    else:
        print("🎉 Correct!")
                

break, continue, pass

break - Exit Early

for i in range(10):
    if i == 5:
        break  # Exit loop completely
    print(i)
# Output: 0, 1, 2, 3, 4
                        

continue - Skip Iteration

for i in range(5):
    if i == 2:
        continue  # Skip this iteration
    print(i)
# Output: 0, 1, 3, 4 (skips 2)
                        

pass - Placeholder

for fruit in fruits:
    if fruit == "banana":
        pass  # TODO: Special handling
    print(fruit)
                

Nested Loops

Multiplication Table

for i in range(1, 6):      # Outer loop
    for j in range(1, 6):   # Inner loop
        print(f"{i} × {j} = {i*j}")
    print("---")  # Separator
                

Pattern Printing

for row in range(5):
    spaces = " " * (4 - row)
    stars = "*" * (2 * row + 1)
    print(spaces + stars)
#     *
#   ***
# *****
# *******
#*********
                

Practice Challenges

1. FizzBuzz Classic

Print numbers 1-100. For multiples of 3 print "Fizz", 5 print "Buzz", both print "FizzBuzz"

2. Number Guessing Game

Generate random number 1-100. Let user guess with hints until correct. Count attempts.

3. Shopping List Manager

While loop menu: add item, remove item, show list, quit. Use list + input validation.

4. Grade Calculator

Input multiple test scores until -1. Calculate average, letter grade, pass/fail.

Infinite Loop Danger!

# ❌ DANGER - Infinite Loop!
count = 0
while count < 5:
    print(count)
    # count += 1  # FORGOT THIS!
                    

Always increment counters or update conditions!

You Can Now Build Real Apps!

🎮 Projects Unlocked:

Number Guessing Game
while + random

Grade Calculator
if/else chains

Todo List
nested loops + menus

Pattern Printer
nested loops mastery

Quiz App
score tracking + conditions

Next: Functions → Data Structures → Complete Projects