Python

nested loops in Python

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nested loops in Python

Definition: A nested loop is a programming concept where one loop is placed inside another loop.

NESTED loop statements:

It’s like putting one loop inside another loop. It’s like doing a task repeatedly within another task. The inner loop runs completely each time the outer loop runs once.

Various types of nested loops:

Nested for loop:

A nested for loop is like putting one for loop inside another. It’s a way to do something repeatedly within another repeated action.

Example –

				
					# Example 1: Multiplication Table
for i in range(1, 6):  # Outer loop
    for j in range(1, 11):  # Inner loop
        product = i * j
        print(f"{i} * {j} = {product}")
    print()  # Add a newline after each table

# Output -
# 1 * 1 = 1
# 1 * 2 = 2
# 1 * 3 = 3
# 1 * 4 = 4
# 1 * 5 = 5
# 1 * 6 = 6
# 1 * 7 = 7
# 1 * 8 = 8
# 1 * 9 = 9
# 1 * 10 = 10

# 2 * 1 = 2
# 2 * 2 = 4
# 2 * 3 = 6
# 2 * 4 = 8
# 2 * 5 = 10
# 2 * 6 = 12
# 2 * 7 = 14
# 2 * 8 = 16
# 2 * 9 = 18
# 2 * 10 = 20

# 3 * 1 = 3
# 3 * 2 = 6
# 3 * 3 = 9
# 3 * 4 = 12
# 3 * 5 = 15
# 3 * 6 = 18
# 3 * 7 = 21
# 3 * 8 = 24
# 3 * 9 = 27
# 3 * 10 = 30

# 4 * 1 = 4
# 4 * 2 = 8
# 4 * 3 = 12
# 4 * 4 = 16
# 4 * 5 = 20
# 4 * 6 = 24
# 4 * 7 = 28
# 4 * 8 = 32
# 4 * 9 = 36
# 4 * 10 = 40

# 5 * 1 = 5
# 5 * 2 = 10
# 5 * 3 = 15
# 5 * 4 = 20
# 5 * 5 = 25
# 5 * 6 = 30
# 5 * 7 = 35
# 5 * 8 = 40
# 5 * 9 = 45
# 5 * 10 = 50

				
					# Example 2: 2D Array

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for row in matrix:  # Outer loop iterates over rows
    for element in row:  # Inner loop iterates over elements in each row
        print(element, end=" ")
    print()  # Move to the next row

# Output -
# 1 2 3 
# 4 5 6 
# 7 8 9

One important use of nested for loops is to print patterns.

				
					# Example 3: Pattern Printing
for i in range(5):  # Outer loop for rows
    for j in range(i + 1):  # Inner loop for columns in each row
        print("*", end=" ")
    print()  # Move to the next row

# Output -
# * 
# * * 
# * * * 
# * * * * 
# * * * * *

Nested if:

Nested-if statements are useful when you need to handle complex branching logic, where certain conditions must be met before others can be evaluated

				
					# Example: Nested If Statements
x = 10
y = 5

if x > y:
    print("x is greater than y")
    if x > 7:
        print("x is also greater than 7")
else:
    print("x is not greater than y")

# Output -
# x is greater than y
# x is also greater than 7

				
					# Example 2: Grading System
score = 85

if score >= 90:
    print("You got an A!")
elif score >= 80:
    print("You got a B.")
    if score >= 85:
        print("You are close to an A.")
else:
    print("You need to improve.")

# Output -
# You got a B.
# You are close to an A.

				
					# Example 3: Divisibility Check
number = 15

if number % 2 == 0:
    print("The number is even.")
    if number % 3 == 0:
        print("The number is also divisible by 3.")
else:
    print("The number is odd.")

# Output -
# The number is odd.

Nested while:

A nested while loop is like putting one while loop inside another. The inner while loop runs completely each time the outer while loop runs once.

Example –

				
					row = 1

while row <= 3:  # Outer loop for rows
    column = 1

    while column <= 4:  # Inner loop for columns
        print("Row", row, "Column", column)
        column += 1

    row += 1

# Output -
# Row 1 Column 1
# Row 1 Column 2
# Row 1 Column 3
# Row 1 Column 4
# Row 2 Column 1
# Row 2 Column 2
# Row 2 Column 3
# Row 2 Column 4
# Row 3 Column 1
# Row 3 Column 2
# Row 3 Column 3
# Row 3 Column 4

In this example,

The outer loop represents rows, and the inner loop represents columns. The code will print combinations of row and column numbers.

The outer loop runs three times for three rows, and the inner loop runs four times for four columns in each row.

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