Last time we wrote programs that ran straight through, line by line. Today our programs will make choices and repeat themselves.

We are coding in Python on the micro:bit. We will build up control structures one step at a time — predict first, then build, run, and fix. Open the Python editor and get your micro:bit ready, but don't type anything yet.

Before anyone runs anything, look at what we are about to build and commit to a prediction.

When the program runs, what will the micro:bit do? What will you see scroll on the display first? Say your prediction to your partner so you can check it in a moment.

In this lesson on control structures, you'll explore the building blocks that allow your programs to make decisions and repeat actions, essential for creating interactive and dynamic code on the Micro:bit. Control structures like conditionals and loops will enable you to respond to inputs, process data, and build more complex programs.

Here's what you'll be learning and doing:

1. Understand conditional statements (if, else, elif) to make decisions based on conditions.
2. Explore nested if statements for handling multi-layered decisions.
3. Learn about loops (for and while) to repeat code efficiently.
4. Discover nested loops and combining loops with conditionals for advanced control.

Conditional statements are a fundamental part of programming that allow your code to make decisions. They let your program execute different blocks of code depending on whether a certain condition is true or false. This is like choosing different paths based on the situation – for example, if it's raining, you might decide to take an umbrella; otherwise, you leave it behind.

The basic building block is the if statement. It checks a condition, and if that condition evaluates to true, the code inside the if block runs. If you want to handle the case when the condition is false, you can add an else clause. For checking multiple conditions, you can use elif (which stands for 'else if') to test additional scenarios.

Conditions are typically built using comparison operators. Here are some common ones:

• == (equal to)
• != (not equal to)
• > (greater than)
• < (less than)
• >= (greater than or equal to)
• <= (less than or equal to)

You can also combine conditions using logical operators like and (both must be true), or (at least one must be true), and not (reverses the condition).

For instance, imagine you're programming a Micro:bit to monitor temperature. You might write code to check if the temperature is above 30 degrees to display a 'Hot' warning, or between 20 and 30 for 'Warm', and below 20 for 'Cool'. This kind of decision-making makes your programs interactive and responsive.

This simple if statement is like a gatekeeper – it only lets the code through if the condition is met. They are the foundation of making decisions in your code. In this step, we'll create a program that checks if a temperature variable is greater than 20 and, if it is, scrolls the message 'Warm' on the display. If the condition isn't met, nothing happens – that's how a basic if works.

We'll start by importing the Micro:bit library, setting a variable, and then using the if statement to check the condition. Remember, indentation is key in Python – the code inside the if must be indented (usually by 4 spaces or by pressing the tab key).

Add the following complete code to your editor:

from microbit import *

temperature = 25

if temperature > 20:
    display.scroll("Warm")