PART 2 • LEVEL 05

🔁 Loops & Patterns

Repeat instructions efficiently, control each iteration and turn simple loop logic into useful number and symbol patterns.

⏱ 90–105 minutes📚 8 concepts💻 5 programs🧠 6-question quiz

Start Lesson ↓Jump to Problems

learning_streak.pyPython 3

total = 0

for day in range(1, 6):
    total += day
    print(f"Day {day}: total = {total}")

print("Streak complete!")

FINAL OUTPUTDay 5: total = 15
Streak complete!

LEARNING OUTCOMES

By the End of This Level

You will be able to choose, trace and control Python loops confidently.

Generate reliable sequences using range().

Use for and while for suitable repetition tasks.

Apply break, continue and nesting correctly.

Construct number and symbol patterns systematically.

REPEAT WITH PURPOSE

Loop Mental Model

A loop repeats a block of code. Each repetition is called an iteration, and a correct loop must know what to repeat and when to stop.

Instead of writing the same statement many times, define one loop body and let Python execute it for a controlled sequence or while a condition remains true.

Iteration

One complete execution of the statements inside a loop body.

1InitializePrepare values

→

2CheckItem or condition

→

3ExecuteRun loop body

→

4UpdateMove forward

GENERATE INTEGERS

The `range()` Function

range() generates an arithmetic sequence of integers. Its stop value is always excluded.

Form	Meaning	Generated values
`range(5)`	Start at 0, stop before 5	`0, 1, 2, 3, 4`
`range(2, 6)`	Start at 2, stop before 6	`2, 3, 4, 5`
`range(2, 11, 2)`	Increase by 2	`2, 4, 6, 8, 10`
`range(5, 0, -1)`	Decrease by 1	`5, 4, 3, 2, 1`

Remember

The step cannot be zero. A negative step requires the start value to be greater than the stop value.

SEQUENCE-CONTROLLED

The `for` Loop

Use for when iterating over a known sequence or a predictable number of values.

EXAMPLE 1

Sum from 1 to 5

total = 0

for number in range(1, 6):
    total += number

print("Sum =", total)

OUTPUT

Sum = 15

Accumulator pattern

Initialize an accumulator such as total before the loop, update it during every iteration, then use the completed value after the loop.

CONDITION-CONTROLLED

The `while` Loop

Use while when repetition depends on a changing condition and the number of iterations is not naturally known in advance.

EXAMPLE 2

Count the Digits

number = 50821
count = 0

while number > 0:
    count += 1
    number //= 10

print("Digits =", count)

OUTPUT

Digits = 5

FOR LOOP

for attempt in range(3):
    print(attempt)

Use it for a known sequence or count.

WHILE LOOP

while balance > 0:
    balance -= payment

Use it while a changing condition remains true.

CONTROL ITERATIONS

`break`, `continue` and `pass`

🛑

`break`

Stops the nearest loop immediately.

⏭️

`continue`

Skips the rest of the current iteration.

🧩

`pass`

Does nothing; it is a valid placeholder statement.

🎯

Nearest Loop

Inside nested loops, control affects only the innermost loop.

EXAMPLE 3

Skip and Stop

for number in range(1, 10):
    if number == 3:
        continue
    if number == 7:
        break
    print(number)

OUTPUT

LOOP INSIDE A LOOP

Nested Loops

For every iteration of the outer loop, the inner loop completes all of its iterations.

EXAMPLE 4

Coordinate Pairs

for row in range(1, 3):
    for column in range(1, 4):
        print(row, column)

OUTPUT

Iteration count

If the outer loop runs 2 times and the inner loop runs 3 times for each outer iteration, the inner body runs 2 × 3 = 6 times.

BUILD ROW BY ROW

Pattern Construction

Treat every pattern as a collection of rows. Decide what changes in each row, then build or print that row inside the loop.

EXAMPLE 5

Growing Star Triangle

stars = ""

for row in range(1, 5):
    stars += "*"
    print(stars)

OUTPUT

*
**
***
****

STEP 1

Count rows

Use the outer loop to choose the current row.

STEP 2

Find row content

Determine how many symbols or numbers belong in that row.

STEP 3

Verify the change

Compare consecutive rows and confirm the intended growth or reduction.

DEBUGGING CORNER

Common Loop Mistakes

Infinite Loop

while count < 5:

Update count so the condition can eventually become false.

Off by One

range(1, 5)

The stop value is excluded, so this produces 1 through 4.

Wrong Scope

total = 0

Initialize accumulators before the loop, not again during every iteration.

Indentation

print(total)

Its indentation decides whether it runs every iteration or once after the loop.

Debug loops:1. Write the starting state2. Test the condition or range3. Trace one iteration4. Confirm the update5. Verify termination

QUICK REVISION

📌 Loops & Patterns — Quick Revision

Review these rules before attempting the quiz and programming problems.

One repetition of a loop body is an iteration.

range() excludes its stop value.

for is natural for sequences and known counts.

while repeats while its condition is true.

A while loop must move toward termination.

break exits the nearest loop.

continue skips to the next iteration.

pass is a placeholder and performs no action.

Nested-loop work multiplies across loop counts.

Patterns become easier when designed row by row.

KNOWLEDGE CHECK

Level 5 Quick Quiz

Select one answer for every question, then check your score.

6 Questions

1What values does range(2, 6) generate?2, 3, 4, 5, 61, 2, 3, 4, 52, 3, 4, 52, 4, 6

2Which loop is usually best when the repetition count is unknown?forwhilematchpass

3What does break do?Stops the nearest loopSkips one statement onlyRestarts the programCreates an empty block

4How many times does for i in range(5): run?46Infinite5

5What must a safe while loop eventually do?Call range()Make its condition falseUse continueContain a nested loop

6An outer loop runs 3 times and its inner loop runs 4 times. How often does the inner body run?371216

PRACTICE

🎯 5 Programming Problems — Loops & Patterns

Follow the CodeBhavya pattern: understand the task, inspect the sample, use the editor, run, check, then compare with the official program.

📈 Loops Practice Progress

Solved0 / 5

Completed with Solution0

Total Score0 / 500

Completion0%

A problem counts as Solved when its output passes before the official solution is opened.

1. Sum of First N Numbers

Read N and calculate the sum from 1 through N.

Sample input: 10Expected output: Sum = 55

💡 Start total at zero and add every value in range(1, n + 1).

Official Python Program

n = int(input())
total = 0
for number in range(1, n + 1):
    total += number
print("Sum =", total)

2. Multiplication Table

Read a number and display its multiplication table from 1 through 10.

Sample input: 7Expected output: Ten lines from 7 x 1 = 7 to 7 x 10 = 70

Official Python Program

number = int(input())
for multiplier in range(1, 11):
    print(number, "x", multiplier, "=", number * multiplier)

3. Count Digits

Read a positive integer and count its digits using a while loop.

Sample input: 50821Expected output: Digits = 5

Official Python Program

number = int(input())
count = 0
while number > 0:
    count += 1
    number //= 10
print("Digits =", count)

4. Factorial

Read a non-negative integer and calculate its factorial.

Sample input: 5Expected output: Factorial = 120

💡 Start the product at 1 and multiply by every number from 1 through n.

Official Python Program

n = int(input())
factorial = 1
for current in range(1, n + 1):
    factorial *= current
print("Factorial =", factorial)

5. Growing Star Pattern

Read the number of rows and display a left-aligned growing star triangle.

Sample input: 4Expected output: Four rows from * through ****

💡 Keep a stars string, add one star each iteration and print the updated row.

Official Python Program

rows = int(input())
stars = ""
for row in range(1, rows + 1):
    stars += "*"
    print(stars)

KEY TAKEAWAY

🎯 Every Loop Needs Progress

1Initialize

Prepare counters and accumulators.

→

2Control

Define the range or condition.

→

3Repeat

Perform one clear iteration.

→

4Terminate

Reach a reliable stopping point.

A strong loop is easy to trace: its starting state is known, every iteration makes progress, and its stopping point is guaranteed.

INTERACTIVE LEARNING

🎬 A `for` Loop — Visual Flow

Watch for number in range(1, 4) select values, execute the body and stop after the sequence is exhausted.

PROGRAM TRACING

🔎 Program Tracing — Accumulator Loop

Trace three iterations and observe how the loop variable, total and output change.

INTERVIEW PREPARATION

🎤 Loops & Patterns — Interview Questions

Answer aloud before opening each explanation.

What is the difference between for and while?

A for loop iterates through a sequence. A while loop repeats while a condition remains true and requires deliberate state updates.

Why is the stop value excluded from range()?

The half-open design makes counts and boundaries predictable: range(n) produces exactly n values starting at zero.

What causes an infinite loop?

How do break and continue differ?

break exits the nearest loop completely. continue skips the remaining statements in the current iteration and moves to the next one.

What is an accumulator?

What is the time complexity of two loops that run n times each when one is nested inside the other?

The inner body runs n × n times, giving quadratic time complexity: O(n²).

EXTRA TIPS

💡 Loops & Patterns — Extra Tips

01
Trace the first two iterations manually before trusting a complex loop.
02
Give counters and accumulators descriptive names instead of using every letter.
03
Check the first value, last included value and excluded stop value of every range.
04
Update a while loop's controlling state visibly inside its body.
05
Avoid unnecessary nesting when one clear condition or formula can solve the task.
06
For patterns, write the expected rows on paper and identify what changes.

EXTRA PRACTICE

✍️ Loops & Patterns — Extra Practice Questions

Display all even numbers from 2 through 100 using range().
Calculate the sum of digits of a positive integer using a while loop.
Reverse a positive integer without converting it to text.
Check whether a number is prime using loop termination when a divisor is found.
Display the first N terms of the Fibonacci sequence.
Count how many values from 1 through 50 are divisible by both 3 and 5.
Build a descending star triangle with five rows.
Build the number pattern 1, 12, 123, 1234.
Use nested loops to display a 3 × 3 coordinate grid.
Trace a deliberately infinite loop and explain the exact missing update.

LEVEL 5 CHECKPOINT

Loops & Patterns Complete

When you can select the right loop, prove its termination and solve all five programs without help, mark this level complete and continue.

Continue to Level 6 →

🔁 Loops & Patterns

By the End of This Level

Loop Mental Model

The range() Function

The for Loop

Sum from 1 to 5

The while Loop

Count the Digits

break, continue and pass

break

continue

pass

Nearest Loop

Skip and Stop

Nested Loops

Coordinate Pairs

Pattern Construction

Growing Star Triangle

Count rows

Find row content

Verify the change

Common Loop Mistakes

📌 Loops & Patterns — Quick Revision

Level 5 Quick Quiz

🎯 5 Programming Problems — Loops & Patterns

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

Python Code Editor

Program Output

Test Case

🎯 Every Loop Needs Progress

🎬 A for Loop — Visual Flow

🔁 How Python Runs a for Loop

1. Create the Sequence

🔎 Program Tracing — Accumulator Loop

🎤 Loops & Patterns — Interview Questions

💡 Loops & Patterns — Extra Tips

✍️ Loops & Patterns — Extra Practice Questions

Loops & Patterns Complete

The `range()` Function

The `for` Loop

The `while` Loop

`break`, `continue` and `pass`

`break`

`continue`

`pass`

🎬 A `for` Loop — Visual Flow

🔁 How Python Runs a `for` Loop