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Loops.md

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Loops

Table of Contents

For and While Loops

For Loops

  • Structure: A for loop is typically used to iterate over a sequence (like a list, tuple, string, or range) or any iterable object.

  • Syntax:

    for variable in sequence:
    # Code block to execute for each item in sequence

  • Example:

    for num in range(5):
    print(num)
    • Output: 0 1 2 3 4
    • Here, range(5) generates a sequence from 0 to 4, and each value is assigned to num in each iteration.

  • Usage: Used when the number of iterations is known, or you need to loop over a collection of items (like lists or strings).

While Loops

  • Structure: A while loop continues to execute as long as its condition remains true.

  • Syntax:

    while condition:
    # Code block to execute while condition is true

  • Example:

    count = 0
while count < 5:
    print(count)
    count += 1
    • Output: 0 1 2 3 4
    • Here, the loop runs as long as count is less than 5. The counter variable count increments in each iteration to avoid an infinite loop.

  • Usage: Used when the number of iterations is unknown and depends on a specific condition being met during runtime.

Loop Control

Break

break terminates the loop immediately, skipping any remaining code in the loop body for that iteration.

Example:

for num in range(10):
    if num == 5:
        break
    print(num)
  • Output: 0 1 2 3 4
  • The loop stops executing when num equals 5.

Continue

continue skips the current iteration and proceeds to the next one, without breaking the loop.

Example:

for num in range(5):
    if num == 2:
        continue
    print(num)
  • Output: 0 1 3 4
  • Here, the iteration with num == 2 is skipped.

Pass

pass is a placeholder that does nothing. It’s useful in loops or conditionals where code will be added later.

Example:

for num in range(5):
    if num == 2:
        pass  # No operation here
    print(num)
  • Output: 0 1 2 3 4
  • pass here serves as a placeholder with no effect on the loop behavior.

Looping Through Different Data Types

  1. Lists
my_list = [1, 2, 3, 4]
for item in my_list:
    print(item)
  • Output: 1 2 3 4 ` Iterates over each element in a list.
  1. Tuples
my_tuple = (5, 6, 7)
for item in my_tuple:
    print(item)
  • Output: 5 6 7
  • Similar to lists, tuples can be iterated with a for loop.
  1. Dictionaries
my_dict = {'a': 1, 'b': 2, 'c': 3}
for key, value in my_dict.items():
    print(f"{key}: {value}")

  • Output:

    a: 1
b: 2
c: 3

  • The items() method allows looping through both keys and values.

  1. Strings
my_string = "hello"
for char in my_string:
    print(char)

  • Output:

    h
e
l
l
o

  • Each character of the string is processed in each loop iteration.

  1. Range
for num in range(3):
    print(num)
  • Output: 0 1 2
  • The range() function creates a sequence of numbers, often used in loops.

Nested Loops and Their Applications

A nested loop is a loop inside another loop. The inner loop runs fully for each iteration of the outer loop.

  • Syntax:

    for i in range(3):        # Outer loop
    for j in range(2):    # Inner loop
        print(i, j)

  • Output:

    0 0
0 1
1 0
1 1
2 0
2 1
    • Here, the inner loop runs twice for every single iteration of the outer loop.

  • Usage:

    Nested loops are commonly used when working with multi-dimensional data, such as a matrix or table:

    matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for row in matrix:
    for value in row:
        print(value)
    • Output: 1 2 3 4 5 6 7 8 9
    • This iterates over each element in a 2D list (matrix).

  • Applications:

    1. Multi-dimensional data (e.g., image data in machine learning, matrix manipulation)
    2. Grid-based games (e.g., navigating a chessboard)
    3. Cartesian products in combinatorics, where each element of one set pairs with each element of another set