Control Flow
Boolean Expressions

In order to build control flow into our program, we want to be able to check if something is true or not. A boolean expression is a statement that can either be True or False.

Let’s go back to the ‘waking up’ example. The first question, “Is today a weekday?” can be written as a boolean expression:

Today is a weekday.

This expression can be True if today is Tuesday, or it can be False if today is Saturday. There are no other options.

Consider the phrase:

Friday is the best day of the week.

Is this a boolean expression?

No, this statement is an opinion and is not objectively True or False. Someone else might say that “Wednesday is the best weekday,” and their statement would be no less True or False than the one above.

How about the phrase:

Sunday starts with the letter 'C'.

Is this a boolean expression?

Yes! This expression can only be True or False, which makes it a boolean expression. Even though the statement itself is false (Sunday starts with the letter ‘C’), it is still a boolean expression.



Determine if the following statements are boolean expressions or not. If they are, set the matching variable to the right to "Yes" and if not set the variable to "No". Here’s an example of what to do:

Example statement:

My dog is the cutest dog in the world.

This is an opinion and not a boolean expression, so you would set example_statement to "No" in the editor to the right. Okay, now it’s your turn:

Statement one:

Dogs are mammals.

Statement two:

My dog is named Pavel.

Statement three:

Dogs make the best pets.

Statement four:

Cats are female dogs.
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