1.6 Scr0360: logical operators in scratch 2.0  (Page 6/7)

Run the program

I encourage you to use the information provided above to write this program. Experiment with the code, making changes, and observing the results of yourchanges. Make certain that you can explain why your changes behave as they do.

Just for fun, see if you can create a startup screen that displays text similar to the title screen or the credits screen at a movie.

I also encourage you to write the programs described below.

Student programming projects

Copies of these two programs have been 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.

The program named Logical02

This Scratch program illustrates the use of relational and logical operators to determine if:

• The value of a variable named LeftOperand is less than or equal to the value of a variable named RightOperand .
• The value of the variable named LeftOperand is greater than or equal to the value of the variable named RightOperand .

The following four variables are created, displayed on the Stage, and set to zero when the user clicks the green flag:

1. LeftOperand (a slider variable)
2. RightOperand (a slider variable)
3. LessThanOrEqual
4. GreaterThanOrEqual

A button is also created and displayed on the Stage as shown in Image H .

Figure

Image h. program output from the program named logical02.

In addition, variables named Equals , GreaterThan , and LessThan are also created but not initialized or displayed. These variables are used by the code to achieve the desired result when the userclicks the button.

The value of each slider variable is set by the user moving the thumb on the slider.

When the user clicks the button, if the left operand is less than or equal to the right operand, the third variable in Image H is set to true. Otherwise, that variable is set to false.

If the left operand is greater than or equal to the right operand, the fourth variable in Image H is set to true. Otherwise it is set to false.

Note, two of the scripts in my version of the program use variables named Equals , GreaterThan , and LessThan whose values are set by the three other scripts. Because I'm unsure as to the orderof execution of the scripts, I inserted a delay of 0.1 second at the beginning of each of those two scripts in an attempt to ensure that the execution of the other threescripts will be completed before an attempt is made to use the values of those variables. This is a crude way to deal with this issue, and is not recommendedfor anything other than demonstration code.

The program named Logical03

This Scratch program is a modification of the program named Logical02. This is a relatively challenging program to write andrequires an understanding of DeMorgan's theorem (see Resources ) .

The behavior of this program is identical to the behavior of the program named Logical02 . However, it is likely that you used the or operator to write that program. This program does not use an or operator.

Instead, this program uses the not operator in conjunction with the and operator along with DeMorgan's theorem to produce behavior that is identical to the program named Logical02 .