Variables

Variables are important in all programming languages and in most programs! Just like in math, variables in programming are placeholders and data storage for numbers. Typically, you can create a variable and save its value at the beginning of your program, and then you can recall that value later on in the program whenever you use the variable.

Let’s go through an example! Sometimes the baud rate for your CoDrone can be hard to remember — is it 112500 or 115200? (It’s 115200) Instead of racking your brain, you can save the baud rate’s value as a variable, which would look like this:

int x = 115200;

Now, 115200 is stored in the variable x! Every time you use x in your program, you can imagine that it’s replaced by 115200.

#include <CoDrone.h>

int x = 115200;

void setup() {
    CoDrone.begin(x);     //same as CoDrone.begin(115200)
    CoDrone.pair();
}

void loop () {
}

There are three steps to using a variable:

1. Initialization – creates the variable in your program
2. Storage – stores the value of your variable
3. Call – uses your variable’s value later in your program

Initializing your variable

Before you use a variable, you have to initialize it. Initialization always follows this format:

DataType VariableName

You can name your variable whatever you want, as long as there are no spaces or special characters. One example is int HappyFace123.

Declaring a value

When you declare a variable, its value is automatically 0. If you don’t want your variable’s value to be equal to 0, you can set an initial value. For example, if you wanted to change HappyFace123‘s value to equal 10, you would need to write:

int HappyFace123 = 10

The scope of a variable is a very important thing to keep in mind when you’re programming. The scope determines where in your program your variable exists. If you try to use a variable outside of its scope, the compiler will show an error saying “not declared in this scope”.

General rule for scope: a variable can only be used within the brackets it’s initialized in.

Here are a few examples:

Example 1

void setup(){ //BRACKET START
//x is initialzed inside the setup's brackets
int x; 
x=2;
}             //BRACKET END

void loop(){
x=1; //running this will give an error
}

void setup(){ 

if(true){//BRACKET START
    int x; 
    x=1;
    }//BRACKET END

x=2; //running this will give an error
}

int x;

void setup(){     
    x=1;
}             

void loop(){
    x=2;
}

Variables in programming can be changed really easily using mathematical operations. Your math teacher will be so excited to hear this!

Mathematical Operations

Addition: x=y+z 

Subtraction: x=y-z 

Multiplication: x=y*z 

Division: x=y/z

Example 1

int y = 4;
int z = 3;
int x = y + z;

int y = 4;
int x = 3;
x = y + x;

Challenge: Variable square

Use the setup code provided to have your CoDrone take off and then fly in a square pattern!

Rules:

1. You are only allowed to use the existing variables, but you can change the values.
2. You can’t use any numbers after you initialize the variables! The only exception is the baud rate.

Setup code

#include <CoDrone.h>

int A = 1;
int B = 500;
int C = 5;
int D = 2;
int E = 10;
int F = 3;

void setup(){  
    CoDrone.begin(115200);  
    CoDrone.pair();

    CoDrone.takeoff();   
}

void loop(){
    byte bt8 = digitalRead(18);
    byte bt4 = digitalRead(14);
    byte bt1 = digitalRead(11);

    if(bt1 && bt4 && !bt8){
        CoDrone.emergencyStop();
    }
}

Example code

#include <CoDrone.h>

int A = 1;
int B = 500;
int C = 5;
int D = 2;
int E = 10;
int F = 3;

void setup(){  
    CoDrone.begin(115200);  
    CoDrone.pair();  

    CoDrone.takeoff();  
    CoDrone.move(D);  

    CoDrone.setThrottle((C * C) * F);  //5 * 5 * 3  = 75; move at 75% power throttle for 2 seconds
    CoDrone.move(A * D);             // 1 * 2 = 2  

    CoDrone.setThrottle(0);          // Zero out the throttle
    CoDrone.move(); 

    CoDrone.land();                    
}

void loop(){
    byte bt8 = digitalRead(18);
    byte bt4 = digitalRead(14);
    byte bt1 = digitalRead(11);

    if(bt1 && bt4 && !bt8){
        CoDrone.emergencyStop();
    }
}