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 time. With your CoDrone, 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 great if you have a lot of values in your program! For example, you might have a program with five different places where you set the speed. Without a variable, you would need to change all five numbers. With a variable, you would only need to change the variable’s value.

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

You’ll be asked to name your variable, and this can be whatever you like! Just make sure it’s something that you’ll remember and that makes sense with what you’re doing.

Once you’re finished creating your variable, the variables menu will have new blocks for you to try out!

One of the blocks you’ll see is set _ to, which will set your variable to whatever value you choose.

To use it, drag it to the top of your code and then go to the gray math menu. From there, you can just use a number value block, or you can use more complex blocks that will make your math teacher super proud of you! 

When you need to recall your variable, or use the information from it, you can use the get block from the variables menu. In Blockly, you will usually end up attaching this block to a loop or conditional. However, you can also set your variables to get the values of other variables! This is useful if you program events that are dependent on each other. 

Try out the example code to see what happens!

If you need to change your variable’s value, you have a couple of options.

To change it throughout the program, you can just type in a new value in the math block next to the set variable block.

If you want to change a variable’s value in just one part of your program, you can use the change by block. Drag the block to where you need it in your program and type in how much you would like to change the variable’s value by. 

Use what you learned to change your CoDrone’s colors! Program your CoDrone so if your variable’s value is less than or equal to 50, your CoDrone’s eyes will turn one color, and if the variable’s value is greater than or equal to 51, your CoDrone’s eyes will turn another color. The LED blocks are in the purple lights menu. 

For an extra challenge, put all of that in a repeat for loop and have your program keep adding one to your variable 100 times. Not sure what a repeat for loop is? Don’t worry! That will be in a later lesson. Just know that whatever blocks are in the loop block will repeat 100 times.

Wondering why the big numbers are needed? Computers can count very quickly so if you use smaller numbers without a wait block, the change in your CoDrone’s LEDs will be very quick. 

Your program might look something like this: 

Challenge: Pin Point 

Program your CoDrone to take off from a landing pad, fly in one direction, and then land on another pad.

Rules:

• You need to use variables in order for your CoDrone to move in one direction and land.
• The starting place and the landing pad shouldn’t change once the challenge has started, but you can change your code after testing it out.
• Don’t forget a kill switch!

If you want to make the challenge more competitive, turn the target into a bullseye and give each section a different point value. The middle of the board should have the highest number of points, and the edges of the board should have the least amount of points.