2.5 Scr0150: relational operators  (Page 5/6)

A screen shot of the program output

Image 6 shows a screen shot of the left portion of the Stage for a given set of values for the variablesnamed LeftOperand and RightOperand .

Figure

Image 6. screen shot of the output from the program named relational01.

Interpretation of the results

The 0 showing in the variable named LessThan tells us that for these values, the following expression evaluates to false:

LeftOperand less than RightOperand

In other words, the left operand (5) is not less than the right operand (-3).

The 0 showing in the variable named Equals tells us that for these values, the following expression evaluates to false:

LeftOperand = RightOperand

In other words, the left operand (5) is not equal to the right operand (-3).

Finally, the 1 showing in the variable named GreaterThan tells us that for these values, the following expression evaluates to true:

LeftOperand greater than RightOperand

In other words, the left operand (5) is greater than the right operand (-3).

If you move the sliders to change the values in the left and right operand variables and then click the button, you are likely to get different results.

An online version of this program is available

A copy of this program has 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 .

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 cause a short drum roll to be produced by your computer speakers each time the button is clicked.

I also encourage you to write the program described below.

Student programming project

Write a project that meets the following specifications:

File name: Relational02.sb

Description: This program illustrates the use of the following relational operators in addition to arithmetic operators:

This is an upgrade to the program named Relational01.sb

The program creates the following six variables and a button and displays them on the screen as shown in Image 7 :

• LeftOperand - a slider
• RightOperand - a slider
• Offset - a slider
• LessThan
• Equals
• GreaterThan

Figure

Image 7. screen shot of the output from the program named relational02.

Operation of the program

When the user clicks the green flag, the values of all six variables shown in Image 7 are set to 0.

The user slides the three sliders to set the values of LeftOperand , RightOperand , and Offset .

When the user clicks the button, three separate event handlers on the button test the sum of the left operand and the offset against the right operand for less than , equal to , and greater than and display the results in the three variables having the corresponding names. A 0 is displayed if the value isfalse and a 1 is displayed if the value is true.