Variables

Variables are found in almost every program that you will come across, including the ones you will be making for your Rokit Smart bots. One of our instructors explains what they are in this video!

Variables are a way to store information in a program. The easiest way to think of them is as if they were different sized boxes. In these boxes, you can store things and then write a name on the box to help you remember what is inside. For example, one box could be named kitchen and have plates in it, while another box could be named books and have books in it.

This variable is named “values” and stores the number 6:

int values = 6;

This variable is named “letters” and stores the letter ‘S’:

char letters = 'S';

You might be asking, “But Robolink! Why do you have “int” and “char”? Why can’t you just use one of them?” The first word tells you what type of information will be stored in the variable, and there are three main types of variables you will be using:

•     int: numbers from -32,768 to 32,767
•     char: letters (actually numbers that are represented by letters, just like algebra!)
•     byte: numbers from -128 to 127

In order to make your life easier, you only need to have the data type labeled when you create the variable. For example:

int values = 6;
values = 4;

The label int isn’t needed the second time around because the variable was already created.

Just like math, variables can be set to other variables:

int a = 1;
int b = a;

But unlike math, variables can be set to themselves:

int values = 6;
values = values + 2;

Below is an example of a program that uses many variables:

// create the variables
int A = 1;
int B = 2;

void setup() {
    Serial.begin(9600); // start the Serial Monitor
}
 
void loop() {
    A = A + 1; // add one to A
    // print out the value of A
    Serial.print("A = "); // prints: A = 
    Serial.println(A); // prints: the value of A

    B = A / 2; // set B to half of A
    // print out the value of B
    Serial.print("B = "); // prints: B = 
    Serial.println(B); // prints: the value of B
    
    // delay to slow it down
    delay(100);
}

This is what’s going on! At the top of the code, variables A and B were created.

• Communication with the serial monitor was started at a baud rate of 9600 in void setup().

There’s a lot going on inside void loop():

• First, 1 is added to A through the loop.
• Then, the value of A is printed in the serial monitor.
• Next, B is set to half of the value of A.
• After that, the value of B is printed on the serial monitor.
• Finally, a short delay of 0.1 seconds, or 100 milliseconds, slows down the loop enough so that you can see what is happening.

If you ran this program as is and watched the serial monitor, you would see A’s value going up by 1 every time, while B’s value would always remain at half of A’s value.