For Loops & Range - Counted Repetition

Card 10 of 15

Repeating a Specific Number of Times

"For loops allow us to continuously change the value of a loop variable. Best for repeating a certain number of times."

Understanding Range

range() generates a sequence of numbers

range(5)

0, 1, 2, 3, 4

Starts at 0, stops before 5

range(2, 7)

2, 3, 4, 5, 6

Starts at 2, stops before 7

range(0, 10, 2)

0, 2, 4, 6, 8

Step by 2 each time

Critical Detail: range() is non-inclusive - it stops BEFORE the end number. If you want numbers 1-10, use range(1, 11).

How For Loops Work

for ii in range(5):
    print(ii)

What's happening:

# Iteration 1: ii = 0
0

# Iteration 2: ii = 1
1

# Iteration 3: ii = 2
2

# Iteration 4: ii = 3
3

# Iteration 5: ii = 4
4

Interactive For Loop Explorer

Start:

Stop:

Step:

Configure range and click Run

For Loop vs While Loop

# For Loop - when you know how many times
for ii in range(5):
    print(ii)

# While Loop - when you don't know
counter = 0
while counter < 5:
    print(counter)
    counter += 1

# Same output, different use cases!

"For loops are cleaner when you know the count. While loops are better when the condition might change in unpredictable ways."

Mental Model: A for loop is like a ticket dispenser. You know exactly how many tickets (iterations) you'll get. The machine automatically counts for you.

Common For Loop Patterns

Count to N: for ii in range(n)
Count from A to B: for ii in range(a, b)
Count by steps: for ii in range(0, 10, 2) # evens
Countdown: for ii in range(10, 0, -1)

                [####################..........] 10/15
            