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CHAPTER 11 — Loops & Repetition - Printable Version

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CHAPTER 11 — Loops & Repetition - Leejohnston - 11-15-2025

Chapter 11 — Loops & Repetition
Loops let your program repeat actions without writing the same code over and over.

There are two main loops in Python:

• for loops — repeat a set number of times 
• while loops — repeat until a condition changes 

---

11.1 The for Loop

A for loop repeats a known number of times.

Example:

Code:
for i in range(5):
    print("Hello")

Output:
Code:
Hello
Hello
Hello
Hello
Hello

range(5) gives: 0, 1, 2, 3, 4

---

11.2 Loop Variable

Inside the loop, i changes each time:

Code:
for i in range(5):
    print(i)

Output:
Code:
0
1
2
3
4

You can rename it:

Code:
for day in range(1, 8):
    print("Day:", day)

---

11.3 range() Variations

Start → End:

Code:
for x in range(3, 8):
    print(x)

Output:
Code:
3
4
5
6
7

Start → End → Step:

Code:
for n in range(0, 20, 5):
    print(n)

Output:
Code:
0
5
10
15

---

11.4 Looping Through Strings

Code:
for letter in "Python":
    print(letter)

---

11.5 Looping Through Lists

Code:
fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)

---

11.6 The while Loop

Repeats while a condition is True.

Code:
count = 1

while count <= 5:
    print(count)
    count += 1

---

11.7 Infinite Loops (Be Careful!)

❌ Warning:

Code:
while True:
    print("Forever")

You must break out manually.

---

11.8 Using break

Stops the loop immediately:

Code:
while True:
    word = input("Type 'stop' to end: ")
    if word == "stop":
        break

---

11.9 Using continue

Skip the current loop and continue with the next one:

Code:
for n in range(1, 8):
    if n == 4:
        continue
    print(n)

Output:
Code:
1
2
3
5
6
7

---

11.10 Practical Pattern — Counting Down

Code:
for n in range(10, 0, -1):
    print(n)
print("Launch!")

---

11.11 Mini Project — Times Tables

Ask user for a number.
Print its times table up to 12.

Code:
7 × 1 = 7
7 × 2 = 14
...
7 × 12 = 84

---

11.12 Challenge — Password Attempt System

Rules:

• user gets 3 attempts 
• password is “python123” 
• use a while loop 
• show attempts left 
• break when successful 
• lock them out after 3 fails 

---

11.13 Chapter Summary

• for loops = repeat a set number of times 
• while loops = repeat until condition changes 
• range() controls the loop 
• break stops early 
• continue skips one loop 
• loops work with lists, numbers, and strings 

Next:
Chapter 12 — Lists: Storing Multiple Items

Lists are like containers that hold many values at once — essential for real programs.

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Written and Compiled by Lee Johnston — Founder of The Lumin Archive