Here is a clear, complete, and exam-ready explanation of Loops in Python, perfect for BCA/MCA/B.Tech students.

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Loops in Python

Loops are used to execute a block of code repeatedly until a condition is met.
Python provides two main types of loops:

1. for loop
2. while loop

Additionally, there are loop control statements:

• break
• continue
• pass

Let’s discuss all of these in detail.

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1. for Loop in Python

A for loop is used to iterate over a sequence (list, string, tuple, dictionary, set) or any iterable object.

Syntax:

for variable in sequence:
    statements

Example 1: Loop through a list

fruits = ["apple", "banana", "mango"]
for item in fruits:
    print(item)

Output:

apple
banana
mango

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Example 2: Loop through a string

for ch in "Python":
    print(ch)

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Example 3: Using range() function

range() generates a sequence of numbers.

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

Output:

0 1 2 3 4

Example:

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

Output:

1 2 3 4 5

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Example 4: Step value

for i in range(1, 10, 2):
    print(i)

Output:

1 3 5 7 9

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2. while Loop in Python

A while loop repeats a block of code as long as the condition is True.

Syntax:

while condition:
    statements

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Example 1: Basic while loop

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

Output:

1 2 3 4 5

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Example 2: Infinite loop

(Only for demonstration — avoid in real programs)

while True:
    print("Running endlessly")

You can stop it by pressing Ctrl + C.

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Example 3: Countdown

n = 5
while n > 0:
    print(n)
    n -= 1

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3. Loop Control Statements

Python provides three keywords to control loops:

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1. break

Stops the loop completely.

Example:

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

Output:

0 1 2 3 4

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2. continue

Skips the current iteration and goes to the next one.

Example:

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

Output:

0 1 2 4 5

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3. pass

Does nothing — used as a placeholder.

Example:

for i in range(5):
    if i == 2:
        pass  # No operation
    print(i)

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4. Nested Loops

A loop inside another loop.

Example: Multiplication table

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

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5. else Block with Loops

Python allows an else block after a loop.
The else part executes only if the loop completes normally (no break).

Example:

for i in range(5):
    print(i)
else:
    print("Loop finished")

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Example with break:

for i in range(5):
    if i == 3:
        break
else:
    print("This will not execute")

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6. Practical Examples

Example 1: Sum of first 10 numbers

total = 0
for i in range(1, 11):
    total += i
print(total)

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Example 2: Reverse a number using while loop

num = 1234
rev = 0

while num > 0:
    rev = rev*10 + num%10
    num //= 10

print("Reversed:", rev)

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Example 3: Print even numbers using for loop

for i in range(1, 21):
    if i % 2 == 0:
        print(i)

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Summary

Loop Type	Use
for loop	Iterate through sequences
while loop	Repeat until condition becomes false
break	Exit loop
continue	Skip iteration
pass	Do nothing (placeholder)
else with loop	Executes if loop ends normally

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