The reason why we have a special data type for booleans, is to make decisions.

We make a decision using the if instruction

An example looks like this

The example above should be read as a pattern that looks something like this

2 If [boolean]:
3   [indented code]
4   [indented code]
5 [code]

The if statement actually controls the current line number, it controls which line the computer should navigate to next.

Let's pretend to be a computer and run our program.

We start at line number 1 and set the value of the variable, isRaining to True. Then we go to line 2.

If the boolean type has the value True, then we go to the next line indented after the if statement, in this example, line number 3.

In our example it is raining, (isRaining is True), so we print a reminder to bring our coat.

We continue onto the next line of code, as long as it has the same level of indentation. Lines of code with the same level of indentation are called a code block.

In our example there’s another line of code with the same indentation so we execute that instruction. We print a reminder to bring an umbrella. When we run out of code with the same indentation, we then start executing the next line with *less indentation. In this example, that's line 5.

Let’s run through that again, but this time, isRaining is False

We start at line 1 and assign False

On line two, we have an if instruction. The boolean type is False so instead of going to line 3, we go to the next line where the indentation is the same as the if instruction.

In our example, that’s line 5.

Since it’s not raining, we don’t get any reminders to bring our coats.

An if statement changes how we execute code, in the code we've worked with so far, we execute all the code. The code under an if statement only gets executed in some cases.