# 1.6 Scr0360: logical operators in scratch 2.0  (Page 2/7)

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## Preview

In this module, I will present and explain a Scratch program named Logical01 . This program illustrates the use of the and , or , and not operators in Scratch. These are called logical operators.

In this module, I will provide an explanation of logical operators and truth tables . Then I will present and explain a Scratch program that illustrates the use of the logical and , or , and not operators when used in conjunction with relational operators. You learned about relational operators in an earlier module.

Finally, I will provide the specifications for two programming projects for you to demonstrate your understanding of what you learned from the first programand from earlier modules. One of the programming projects is relatively difficult requiring an understanding of DeMorgan's theorem .

Copies of all three programs will be posted online for your review (see Resources for the URL) . If you don't find the program using that URL, search the Scratch site for the usernamed dbal .

## A real-world example

Logical operators can be confusing at first glance, but perhaps a real world example will help to eliminate some of that confusion. For many years in thiscountry, we have had a movie rating system designed to control the viewing of objectionable content by young people. According to Wikipedia , the R rating means something like the following:

"Restricted - Under 17 requires accompanying parent or adult 17 or older with photo ID"

## Formulate this using logical operator concepts

In most cases, this means that a person will be allowed entry into the theatre to view the movie if:

• The person has the price of admission and is older than 16, or
• The person has the price of admission and is under 17 and is accompanied by an adult who also has the price of admission and the adult can show a photo ID.

Note the use of the boldface Italicized words or and and in the above example.

## The not operator

The not operator is a little more difficult to explain in terms of real world examples. At this point, suffice it to say that the application ofthe not operator causes something that is true to become false and causes something that is false to become true. For example, if someone is older than16, that person is not 16 or younger.

## The reality - logic in a formal sense

The reality is that you have been dealing with this kind of logic most of your life. However, unless you had a specific reason to do so, such as being acomputer programmer, a computer engineer, or perhaps an attorney, you may never have thought about it in a formal sense. The time to think about it in a formalsense has arrived.

## A button and s even variables

This program creates a button along with the following seven variables.

```A (a slider variable) B (a slider variable)C (a slider variable) D (a slider variable)A<B and C<D not(A<B and C<D) A<B or C<D```

The program displays the button and the variables on the Stage and initializes all of the variables to zero when the user clicks the green flag asshown in Image A .

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