07.Loops.md

Loops in Python

(for Loop and while Loop)

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1. Introduction

Sometimes we need to repeat a task multiple times.

Examples:

• Print numbers from 1 to 10
• Print a message 5 times
• Check numbers one by one
• Process multiple inputs

Instead of writing the same code again and again, we use loops.

Loops allow us to execute a block of code repeatedly.

There are two main loops in Python:

1. for loop
2. while loop

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2. The for Loop

The for loop is mainly used when we know how many times we want to repeat something.

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Using range()

range() is commonly used with for loop.

Example 1: Print 1 to 5

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

Output:

1
2
3
4
5

Important:

• Start value is included
• End value is excluded

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Different Forms of range()

1. range(stop)

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

Output:

0
1
2
3
4

2. range(start, stop)

for i in range(2, 6):
    print(i)

3. range(start, stop, step)

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

Output:

1
3
5
7
9

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Looping Through a String

text = "Python"

for ch in text:
    print(ch)

This prints each character one by one.

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3. The while Loop

The while loop runs as long as the condition is True.

Syntax:

while condition:
    statement

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Example: Print 1 to 5

i = 1

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

Important:

• Always update the variable inside the loop
• Otherwise, it becomes an infinite loop

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Infinite Loop Example (Wrong)

i = 1

while i <= 5:
    print(i)

This will run forever because i never changes.

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4. Loop Control Statements

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break

Stops the loop completely.

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

Output:

1
2
3
4

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continue

Skips the current iteration.

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

Output:

1
2
4
5

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5. Difference Between for and while

Use for loop when:

• Number of repetitions is known

Use while loop when:

• Repetition depends on a condition

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6. Common Beginner Mistakes

1. Forgetting to update variable in while loop
2. Wrong indentation
3. Using incorrect range values
4. Creating accidental infinite loops

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7. Practice Exercises

1. Print numbers from 1 to 20
2. Print even numbers from 1 to 20
3. Print multiplication table of a number
4. Count from 10 down to 1
5. Print each character of a word

Example:

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

for i in range(1, 11):
    print(num * i)

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