Step 6¶

In Step 6, we will focus on problem-solving using control structures. This step will build on the concepts of conditional statements and introduce loops, which are essential for creating dynamic and efficient programs.

Problem-Solving with Control Structures¶

Control structures allow us to control the flow of our programs, making them more dynamic and responsive to different inputs and conditions. In this step, we will explore how to use control structures to solve problems.

Loops in Python¶

Loops are used to execute a block of code repeatedly. Python provides two types of loops: for loops and while loops.

The `for` Loop¶

The for loop is used to iterate over a sequence of numbers and execute a block of code for each number.

lists in Python

A list is a collection of items that can be of different types. You can create a list by placing the items inside square brackets [], separated by commas. For example:

numbers_list = [1, 2, 3, 4, 5]

Lists are iterable, meaning you can loop over the items in a list using a for loop. Python makes great use of lists and other iterable objects to simplify programming tasks!

Syntax¶

numbers_list = [1, 2, 3, 4, 5]

for number in numbers_list:
    # code block to be executed for each number in the list

Example¶

numbers_list = [1, 2, 3, 4, 5]
for number in numbers_list:
    print(number)

The range() Function

The range() function is commonly used with for loops to generate a sequence of numbers. It takes three arguments: start, stop, and step. For example, range(1, 6, 2) generates the sequence 1, 3, 5.

You can also use range() with a single argument to generate a sequence starting from 0. For example, range(5) generates the sequence 0, 1, 2, 3, 4.

You can use the range() function to iterate over a specific range of numbers in a for loop, like this:

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

Another Example¶

Just like you can loop over a list of numbers, you can loop over a string in Python. When you feed in a string to a for loop, it will iterate over each character in the string.

for character in "This will print vertically":
    print(character)

The `while` Loop¶

The while loop is used to execute a block of code as long as a condition is true.

Syntax¶

while condition:
    # code block to be executed as long as the condition is true

Example¶

count = 0
while count < 3:
    print(count)
    count += 1

The += Operator

The += operator is used to increment (add) the value of a variable. This is a shorter way to write

variable = variable + 1

-= can be used to decrement (subtract) the value of a variable, as well as *=, /=, and **= for multiplication, division, and exponentiation, respectively.

Combining Loops and Conditional Statements¶

You can combine loops and conditional statements to create more complex control structures.

Example¶

numbers_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
for i in numbers_list:
    if i % 2 == 0:
        print(f"{i} is even")
    else:
        print(f"{i} is odd")

Exercise: Problem-Solving with Control Structures¶

Now it's time to practice using loops and conditional statements to solve problems. You can do this in your own Colab Notebook, in an .ipynb file in VSCode, or in a Python file in VSCode.

Exercise 1: Simple Loops¶

Write a Python program that prints the numbers from 1 to 5 using a for loop, then do it again for a while loop.

Solution

Here's a simple solution to the simple loops problem:

# Using a for loop
numbers_list = [1, 2, 3, 4, 5]
for i in numbers_list:
    print(i)

# Using a while loop
count = 1
while count < 6:
    print(count)
    count += 1

Exercise 2: Sum of Numbers¶

Write a Python program that calculates the sum of numbers from 1 to 10.

Hint

You can use a for loop combined with the range() function to iterate over the numbers from 1 to 10 and calculate the sum. You could also implement the += operator to increment the sum for each number.

Solution

Here's a simple solution to the sum of numbers problem:

total = 0
for i in range(1, 11):
    total += i
print(f"The sum of numbers from 1 to 10 is: {total}")

Exercise 3: FizzBuzz¶

Write a Python program that prints the numbers from 1 to 20. For multiples of three, print "Fizz" instead of the number, and for the multiples of five, print "Buzz". For numbers which are multiples of both three and five, print "FizzBuzz".

Solution

Here's a simple solution to the FizzBuzz problem:

for i in range(1, 21):
    if i % 3 == 0 and i % 5 == 0:
        print("FizzBuzz")
    elif i % 3 == 0:
        print("Fizz")
    elif i % 5 == 0:
        print("Buzz")
    else:
        print(i)

Exercise 4: Counting Vowels¶

Write a Python program that counts the number of vowels in a given string.

Hint

You can use a for loop to iterate over each character in the string and a conditional statement to check if the character is a vowel.

Solution

Here is one solution to the problem:

string = "This is a sample string"
vowels = "aeiouAEIOU"
count = 0
for char in string:
    if char in vowels:
        count += 1
print(f"The number of vowels in the string is: {count}")

Exercise 5: Reverse a String¶

Write a Python program that reverses a given string using a for loop.

Hint

You can use a for loop to iterate over the string in reverse order and build a new string.

Solution

Here's a possible solution:

string = "Hello, World!"
reversed_string = ""
for char in string:
    reversed_string = char + reversed_string
print(f"The reversed string is: {reversed_string}")

Think: Why does this solution work?

Exercise 6: Multiplication Table with F-Strings¶

Write a Python program that generates a multiplication table for numbers 1-5, using f-strings.

Hint

You can use nested for loops to generate the multiplication table for numbers 1-5.

Solution

Here's a possible solution:

for i in range(1, 6):
    for j in range(1, 6):
        print(f"{i} x {j} = {i * j}") # Print a new line after each row

This solution uses nested for loops to generate the multiplication table for numbers 1-5. The outer loop iterates over the numbers 1-5 for the first multiplier, and the inner loop iterates over the numbers 1-5 again for the second number, generating a table of all multiplication results.

Reflect¶

Think about how loops and conditional statements can be used to solve problems. What are some real-world scenarios where these concepts might be useful?

Automating Repetitive Tasks

Loops and conditional statements are essential for automating repetitive tasks and handling different conditions in programs. For example, you can use loops to process large datasets, iterate over files in a directory, or perform calculations based on specific conditions. Conditional statements can be used to control the flow of a program, handle user inputs, or make decisions based on certain criteria.

Another tool, functions, can also be used to automate repetitive tasks. We'll learn about functions in the next step!

Review¶

In this step, we learned about loops and how to use them in combination with conditional statements to solve problems. Here's a quick recap:

for Loop: Used to iterate over a sequence of numbers and execute a block of code for each number.
while Loop: Used to execute a block of code as long as a condition is true.
Combining Loops and Conditional Statements: Allows for more complex control structures and problem-solving.

Understanding these concepts is essential for writing dynamic and efficient programs in Python.

Step 6¶

Problem-Solving with Control Structures¶

Loops in Python¶

The for Loop¶

Syntax¶

Example¶

Another Example¶

The while Loop¶

Syntax¶

Example¶

Combining Loops and Conditional Statements¶

Example¶

Exercise: Problem-Solving with Control Structures¶

Exercise 1: Simple Loops¶

Exercise 2: Sum of Numbers¶

Exercise 3: FizzBuzz¶

Exercise 4: Counting Vowels¶

Exercise 5: Reverse a String¶

Exercise 6: Multiplication Table with F-Strings¶

Reflect¶

Review¶

The `for` Loop¶

The `while` Loop¶