Jan 53 min read

Day 4 - Control Flow - If statements and loops

Hello friends, welcome back! Today, on Day 4 of our Python journey, we will be exploring the control flow, where the magic happens. Brace yourselves as we explore the fascinating world of if statements and loops, the architects of decision-making and repetition in Python.

Getting Our Hands Dirty: Installing Python on Ubuntu

Before we dive into the wonders of control flow, let's ensure we have Python up and running on our Ubuntu system. Open your terminal and type the following command:

sudo apt update
sudo apt install python3

Once the installation is complete, you can check if Python installed successfully by typing:

python3 --version

Now, armed with Python, let's embark on our journey of understanding control flow.

If Statements: Making Decisions in Python

Imagine you're writing a program, and you want it to make decisions based on certain conditions. This is where if statements come to the rescue. They allow your program to take different paths depending on whether a condition is true or false.

Let's take a simple example. Suppose we want to check if a number is positive or negative. In Python, it looks something like this:

# Example 1: Positive or Negative
number = 5
if number > 0:
    print("The number is positive.")
else:
    print("The number is negative.")

In this snippet, we use the if keyword to check if number is greater than 0. If the condition is true, the indented code block beneath it executes. Otherwise, the code block under else runs.

Loops: Embracing Repetition

Loops are the superheroes of automation in programming. They allow us to repeat a set of instructions multiple times, saving us from writing the same code over and over again. Let's explore two popular types of loops: for and while.

For Loop: Taming Sequences

The for loop is perfect for iterating over sequences like lists, strings, or ranges. Here's a simple example of printing numbers from 1 to 5 using a for loop:

# Example 2: For Loop
for i in range(1, 6):
    print(i)

In this snippet, the range(1, 6) generates a sequence from 1 to 5, and the for loop iterates over it, printing each number.

While Loop: The Persistent Worker

The while loop continues iterating as long as a specified condition is true. Let's create a simple countdown using a while loop:

# Example 3: While Loop
countdown = 5
while countdown > 0:
    print(countdown)
    countdown -= 1

In this example, the loop prints the countdown value while it's greater than 0, decrementing it with each iteration.

Bringing It All Together: A Real-world Example

Now, let's combine our knowledge of if statements and loops to solve a real-world problem. Suppose we want to find the sum of all even numbers between 1 and 10. Here's how we can do it:

# Example 4: Sum of Even Numbers
sum_of_evens = 0
for num in range(1, 11):
    if num % 2 == 0:
        sum_of_evens += num
print("Sum of even numbers:", sum_of_evens)

In this script, we use a for loop to iterate over the range from 1 to 10. Inside the loop, an if statement checks if the current number is even (num % 2 == 0). If true, we add it to our sum_of_evens variable.

Congratulations on making it through Day 4 of our Python adventure! Today, we explored the powerful world of control flow, understanding how if statements and loops shape the flow of our programs. From making decisions to embracing repetition, these tools are indispensable in any Python programmer's toolkit.

Take a moment to experiment with different conditions and loops, and don't hesitate to modify our examples to see how they behave. The more you practice, the more comfortable you'll become with these fundamental concepts.

Stay tuned for Day 5, where we'll delve into functions and modules, another crucial aspect of Python programming.

Happy coding!

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