1.4: Variables

Variables are a way to store information in a program, and they’re used most often to store values. If you’re playing a video game, there’s a variable to store your score, another one for your lives, and maybe another one for experience points. With your CoDrone EDU, you might use them to store the value of a sensor, the speed of your drone, or maybe how far it will go.

Variables are especially beneficial if a value appears multiple times in your program. Take a look at the following square code from the previous lesson. What would you have to do to make the square bigger? How can a variable solve this problem?

To create a variable, go to the pink variables menu in Blockly and click on the Create variable… button.

Next, you have to name your variable. In programming, it is important that your variable name is short and descriptive. For now, we will use a common variable you have probably used in your math class before. Name your variable “x”.

For every new variable you create, you will see a set of blocks created in the “Variables” menu for you to use.

To initialize a variable means to assign the variable to a value. In this course, you will normally set variables to a number, but there are other variable types as well that you will learn about in a future lesson. Drag the set block with your variable to the workspace.

Set the variable “x” to a number by accessing the “Math” menu and dragging in the number block.

Then, change the 0 value to any number.

When you need to use the value that is stored in the variable, you can use the block with the variable name. Open the menu and find the “get” block. Use the dropdown menu to select your variable.

A good tool to know for debugging variable values is the print block. The print block can be found inside the “Input/Output” menu.

Connect a variable or any block that returns a value to see the value in the console window. Add a print block to your program and connect it to the block that retrieves the “y” value.

Now that you know the basics of using variables, let’s use variables to improve the square program. Open or create a program that will fly CoDrone EDU in a square shape. Use the default go values like this:

Run your code and observe its behavior. Then, create a new variable “seconds” and set it to 1 at the top of your square program.

Find every part in your code that uses the number 1 to program a flight duration. Now that you have a variable, you can replace each of these duration parameters with the variable block for seconds. Drag and drop the variable block directly into the seconds parameter.

Now, repeat for all seconds parameters.

Run the code again and notice that it runs the exact same way as before!

What would you do to make the square bigger? In the original program without variables, you would need to change every go block. Now, you only need to change the variable value, and it will be applied for the entire program. Make the square bigger by changing the value to 2. Make sure to clear a space that’s large enough for your new flight path.

To change a variable value in the middle of a program without user input, you can use the change by block. This block will increase or decrease the value of the variable by the number you input. For example, this program increases the length of each side by 0.5 seconds for each side of the square. Draw the flight path on paper. What does it look like?

From your square program, add other variables for duration, power, and degrees. What kinds of flight patterns can you create?