04-03-ControlFlow(for loop).md

for Loop in Python:

The for loop in Python is used to iterate over a sequence of items, executing a block of code for each item in the sequence. It is a versatile and powerful tool for performing repetitive tasks efficiently.

Syntax:

for item in sequence:
    # Code block to execute for each item
    statement1
    statement2
    ...

Explanation:

• The for keyword initiates the loop.
• item is a variable that represents each item in the sequence during each iteration of the loop.
• sequence is any iterable object that contains the items to iterate over, such as a string, range, or other iterable.
• The code block indented under the for statement is executed for each item in the sequence.

Using the in Operator:

• The in operator is used to check for the presence of an item in a sequence.
• It returns True if the item is found in the sequence, and False otherwise.

Using the range() Method:

• The range() method is used to generate a sequence of numbers within a specified range.
• It takes up to three arguments: start, stop, and step.
• start (optional): The starting value of the range (default is 0).
• stop: The end value of the range (exclusive).
• step (optional): The increment between each number in the range (default is 1).

Example: Printing Numbers from 1 to 5

for num in range(1, 6):  # Range from 1 to 5 (inclusive start, exclusive end)
    print(num)

Explanation:

• In this example, the range(1, 6) method generates a sequence of numbers from 1 to 5.
• The for loop iterates over each number in the sequence, assigning it to the variable num during each iteration.
• The print(num) statement prints each number in the sequence.

Example: Summing Numbers from 1 to 10

total = 0
for num in range(1, 11):  # Range from 1 to 10 (inclusive start, exclusive end)
    total += num

print("Sum of numbers from 1 to 10:", total)

Explanation:

• In this example, the total variable is initialized to 0.
• The for loop iterates over each number in the sequence generated by range(1, 11).
• During each iteration, the current number is added to the total variable.
• After the loop completes, the total sum of numbers from 1 to 10 is printed.

Using input() and Type Casting:

n = int(input("Enter the number of iterations: "))
for i in range(n):
    print("Iteration", i+1)

Explanation:

• In this example, the user inputs the number of iterations (n) for the loop using the input() method.
• The input string is converted to an integer using the int() function to determine the range for the loop.
• The loop iterates n times, with i ranging from 0 to n-1.
• Each iteration number is printed, starting from 1.

Key Points:

• The for loop is used to iterate over a sequence of items.
• The in operator checks for the presence of an item in a sequence.
• The range() method generates a sequence of numbers within a specified range.
• Proper indentation is crucial for defining the code block inside the loop.
• input() and type casting can be used to make the loop more interactive, allowing user input to control the loop's behavior.

Nested for Loop:

Nested loops in Python refer to the situation where you have one loop (inner loop) inside another loop (outer loop). This structure allows you to iterate over elements in a more complex manner, often useful for iterating through multidimensional data structures like matrices or nested lists.

Syntax:

for outer_item in outer_sequence:
    for inner_item in inner_sequence:
        # Code block to execute for each inner item
        statement1
        statement2
        ...
    # Code block to execute after inner loop completes (optional)
    statement3
    statement4
    ...
# Code block to execute after outer loop completes (optional)
statement5
statement6
...

Explanation:

• The outer loop iterates over each item in the outer sequence.
• For each iteration of the outer loop, the inner loop iterates over each item in the inner sequence.
• The code block inside the inner loop is executed for each combination of outer and inner items.
• After completing the inner loop for each outer item, the code block after the inner loop (if present) is executed.
• Finally, after completing all iterations of the outer loop, the code block after the outer loop (if present) is executed.

Example: Multiplication Table

Let's use nested loops to generate a multiplication table:

for i in range(1, 11):
    for j in range(1, 11):
        print(i, "x", j, "=", i * j)
    print()  # Print a blank line after each row

Explanation:

• The outer loop (for i in range(1, 11)) iterates over the multiplicand (numbers from 1 to 10).
• For each value of i, the inner loop (for j in range(1, 11)) iterates over the multiplier (also numbers from 1 to 10).
• Inside the inner loop, the product of i and j is calculated and printed as a part of the multiplication table.
• After each row (i.e., after completing the inner loop for a specific i), a blank line is printed to separate the rows visually.

Example: Pattern Printing

Nested loops can also be used to print patterns, such as a triangle:

rows = 5
for i in range(1, rows + 1):
    for j in range(1, i + 1):
        print("*", end=" ")
    print()  # Move to the next line after each row

Explanation:

• The outer loop controls the number of rows to be printed.
• The inner loop controls the number of stars (*) to be printed in each row.
• The number of stars in each row is equal to the row number (i) in the outer loop.
• After printing the stars for each row, the inner loop moves to the next line (print() statement) to start a new row.

Key Points:

• Nested loops are useful for iterating over multidimensional data structures or for performing repetitive tasks that require multiple levels of iteration.
• Pay attention to proper indentation to maintain the hierarchy of the loops and the associated code blocks.
• Nested loops can have any number of levels, but excessive nesting should be avoided for the sake of code readability and maintainability.