NESTED FOR LOOP IN PYTHON

📘 Nested for Loop in Python (Easy Explanation + Examples)

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🎯 What is Nested for Loop?

A nested for loop means a for loop inside another for loop.

It is used when we need to work with:

• patterns
• tables
• matrices
• grids
• repeated combinations

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📌 Definition

A nested for loop is a loop where one for loop is placed inside another for loop to perform repeated iteration of iterations.

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🧠 Syntax

for i in range(n):
    for j in range(m):
        # code block

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🔁 How It Works

• Outer loop runs first
• For each outer loop, inner loop runs completely
• Then outer loop moves to next iteration

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📊 Example 1: Simple Nested Loop

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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📊 Example 2: Multiplication Table

for i in range(1, 6):
    for j in range(1, 11):
        print(i * j, end=" ")
    print()

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📊 Example 3: Star Pattern (Rectangle)

for i in range(1, 5):
    for j in range(1, 6):
        print("*", end=" ")
    print()

Output:

* * * * *
* * * * *
* * * * *
* * * * *

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📊 Example 4: Right Angle Triangle Pattern

for i in range(1, 6):
    for j in range(1, i+1):
        print("*", end=" ")
    print()

Output:

*
* *
* * *
* * * *
* * * * *

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📊 Example 5: Number Pattern

for i in range(1, 5):
    for j in range(1, i+1):
        print(j, end=" ")
    print()

Output:

1
1 2
1 2 3
1 2 3 4

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📊 Example 6: Matrix Printing

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

for i in matrix:
    for j in i:
        print(j, end=" ")
    print()

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⚡ Advantages of Nested for Loop

• Useful for patterns
• Works with matrices
• Handles multiple iterations
• Very important for exams

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❌ Disadvantages

• Can be slow for large data
• Complex if deeply nested
• Hard to debug

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🧠 Real-Life Examples

• Chess board ♟️
• Calendar system 📅
• Table/grid display 📊
• Matrix operations 🧮

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📘 Summary

• Nested for loop = loop inside loop
• Outer loop controls rows
• Inner loop controls columns
• Used in patterns, tables, matrices

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🧠 Important Questions

Short Questions

1. What is nested for loop?
2. Write syntax of nested for loop.
3. Give one example.
4. What is outer loop?
5. What is inner loop?

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Long Questions

1. Explain nested for loop with example.
2. Write program for star pattern.
3. Write program for multiplication table using nested loop.
4. Explain matrix printing using nested loop.
5. Write number pattern program.

📘 20 Pattern Programs Using Nested for Loop (Python)

These are very important exam + viva + coding questions.

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⭐ 1. Square Pattern

for i in range(5):
    for j in range(5):
        print("*", end=" ")
    print()

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⭐ 2. Right Triangle Star Pattern

for i in range(5):
    for j in range(i+1):
        print("*", end=" ")
    print()

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⭐ 3. Reverse Right Triangle

for i in range(5, 0, -1):
    for j in range(i):
        print("*", end=" ")
    print()

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⭐ 4. Number Triangle

for i in range(1, 6):
    for j in range(1, i+1):
        print(j, end=" ")
    print()

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⭐ 5. Same Number Triangle

for i in range(1, 6):
    for j in range(i):
        print(i, end=" ")
    print()

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⭐ 6. Continuous Number Pattern

num = 1
for i in range(4):
    for j in range(4):
        print(num, end=" ")
        num += 1
    print()

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⭐ 7. Inverted Number Triangle

for i in range(5, 0, -1):
    for j in range(1, i+1):
        print(j, end=" ")
    print()

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⭐ 8. Pyramid Star Pattern

for i in range(5):
    print(" " * (5 - i), end="")
    for j in range(i + 1):
        print("* ", end="")
    print()

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⭐ 9. Inverted Pyramid

for i in range(5, 0, -1):
    print(" " * (5 - i), end="")
    for j in range(i):
        print("* ", end="")
    print()

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⭐ 10. Diamond Pattern (Simple)

for i in range(5):
    print(" " * (5 - i), end="")
    for j in range(i + 1):
        print("* ", end="")
    print()

for i in range(4, 0, -1):
    print(" " * (5 - i), end="")
    for j in range(i):
        print("* ", end="")
    print()

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⭐ 11. Alphabet Pattern (A)

for i in range(5):
    for j in range(i+1):
        print(chr(65 + j), end=" ")
    print()

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⭐ 12. Repeated Alphabet

for i in range(5):
    for j in range(i+1):
        print(chr(65 + i), end=" ")
    print()

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⭐ 13. Floyd’s Triangle

num = 1
for i in range(5):
    for j in range(i+1):
        print(num, end=" ")
        num += 1
    print()

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⭐ 14. 0-1 Pattern

for i in range(5):
    for j in range(i+1):
        print((i + j) % 2, end=" ")
    print()

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⭐ 15. Hollow Square

n = 5

for i in range(n):
    for j in range(n):
        if i == 0 or i == n-1 or j == 0 or j == n-1:
            print("*", end=" ")
        else:
            print(" ", end=" ")
    print()

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⭐ 16. Hollow Triangle

for i in range(5):
    for j in range(i+1):
        if j == 0 or j == i or i == 4:
            print("*", end=" ")
        else:
            print(" ", end=" ")
    print()

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⭐ 17. Right Pascal Triangle

for i in range(5):
    for j in range(i+1):
        print("*", end=" ")
    print()

for i in range(4, 0, -1):
    for j in range(i):
        print("*", end=" ")
    print()

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⭐ 18. Left Triangle

for i in range(5):
    print("  " * (5 - i), end="")
    for j in range(i+1):
        print("*", end=" ")
    print()

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⭐ 19. Number Pyramid

for i in range(5):
    print(" " * (5 - i), end="")
    for j in range(i+1):
        print(j+1, end=" ")
    print()

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⭐ 20. Full Pyramid Numbers

for i in range(1, 6):
    print(" " * (5 - i), end="")
    for j in range(1, i+1):
        print(j, end=" ")
    for j in range(i-1, 0, -1):
        print(j, end=" ")
    print()