📘 Lesson 6 examples: Loops in Python

🔹 1. What is a Loop?

A loop is used to repeat a block of code multiple times.

👉 Without loops → code becomes long
👉 With loops → code becomes short & clean

Python has mainly two loops:

• for loop
• while loop

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🔹 2. for Loop

A for loop is used when number of repetitions is known.

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Example 1: Printing Numbers

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

Output

0
1
2
3
4

📌 Explanation

• range(5) generates numbers from 0 to 4
• Loop runs 5 times

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Example 2: Printing Numbers from 1 to 5

for i in range(1, 6):
    print(i)

Output

1
2
3
4
5

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Example 3: Printing Names

names = ["Sameer", "Ayesha", "Saddam", "Chandini"]

for name in names:
    print(name)

Output

Sameer
Ayesha
Saddam
Chandini

📌 Explanation

• Loop runs once for each item in the list

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🔹 3. range() Function

Syntax	Meaning
range(stop)	0 to stop-1
range(start, stop)	start to stop-1
range(start, stop, step)	step increment

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Example 4: Step Value

for i in range(1, 11, 2):
    print(i)

Output

1
3
5
7
9

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🔹 4. while Loop

A while loop runs as long as a condition is true.

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Example 5: Print Numbers Using while

i = 1

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

Output

1
2
3
4
5

📌 Explanation

• Condition checked before every iteration
• If condition becomes False, loop stops

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🔹 5. Infinite Loop (IMPORTANT)

while True:
    print("Hello")

⚠ This loop never stops unless manually interrupted.

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🔹 6. break Statement

Used to stop the loop immediately.

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Example 6: Stop Loop When Condition Met

for i in range(1, 10):
    if i == 5:
        break
    print(i)

Output

1
2
3
4

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🔹 7. continue Statement

Used to skip the current iteration.

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Example 7: Skip a Number

for i in range(1, 6):
    if i == 3:
        continue
    print(i)

Output

1
2
4
5

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🔹 8. else with Loops

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Example 8: Loop with else

for i in range(3):
    print(i)
else:
    print("Loop completed")

Output

0
1
2
Loop completed

📌 Explanation

• else runs when loop ends normally
• It does NOT run if break is used

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🔹 9. Nested Loops (Loop inside Loop)

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Example 9: Number Pattern

for i in range(1, 4):
    for j in range(1, 4):
        print(i, j)

Output

1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3

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🔹 10. Real-Life Example: Multiplication Table

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Example 10

number = int(input("Enter a number: "))

for i in range(1, 11):
    print(number, "x", i, "=", number * i)

Sample Output

Enter a number: 5
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

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🔹 11. Common Mistakes (IMPORTANT)

❌ Forgetting to update condition in while loop
❌ Wrong indentation
❌ Infinite loops accidentally
❌ Using break incorrectly

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🧠 Final Summary

✔ for loop → fixed number of times
✔ while loop → condition-based
✔ range() controls repetition
✔ break stops loop
✔ continue skips iteration
✔ Nested loops handle complex logic