Return Functions

You’ve already learned about functions — they’re blocks of code that can be named and reused in different parts of your program. Return functions also do this, but they also return a value to your program. One real-life example is turning in your homework. The input to the function would be your answers to the homework. The function would calculate the number of correct answers and return that value.

This is what a return function usually looks like:

ReturnDataType FunctionName(inputs){ 
    statements;
    return ReturnValue;
}

This is what’s going on here:

• ReturnDataType is the type of data that will be returned. If you don’t remember the data types, check the Variables lesson.
• FunctionName is the name of the function. This can be whatever you want!
• Inputs are anything that the function needs to run. This could be a duration of time, the LEDs that should light up, the drone to connect to, or in some cases, like with CoDrone.move(), nothing at all.
• Statements are the code that will run when the function is called.
• return is the command that will exit out of the function and return the value to you.
• ReturnValue is the value that will be returned to you in the program. Make sure it matches up with the data type you wrote in ReturnDataType!

So if you were to write a function that would return the number of correct answers, this is what it could look like:

int getHomeworkGrade(int answers){
    count number of correct answers
    return number of correct answers  
}

Ready to write your own return function? Try one that will do math for you! This function will accept two whole numbers, multiply them together, and return the answer:

int Mult(int x, int y){
    int z = x * y; 
    return z;
}

Here are some examples of other functions that return values.

max() takes two numbers as input and returns the larger of the two. In this case, since 100 is larger than 20, 100 would be returned.

int Max(int x, int y){
  if (x > y) {
    return x;
  }
  else {
    return y;
  }
}

int Min(int x, int y){
    if (x < y) {
        return x;
    }
    else {
        return y;
    }
}

int MinNum = Min(100,20);

Calling a return function is a little different than calling a void function (and if you forgot what a void function looks like, go back to the lesson Void Functions). Instead of writing a function and then using its name in your program, the setup looks similar to how you would declare a variable. This is because the return value needs to be stored. Make sure the data type of your variable matches the return data type of the function!

For example, if you wrote a function to read the value of your joystick (anywhere from 0 to 1023) and return it, this is what it would look like:

int x = analogRead(23);

For this lesson, you’re going to write a program to have your CoDrone’s arms change color while it spins! The beginning of the program should include the library.

Above void setup, you need to write a function definition that will return a random number (we called ours RandomNum). In that function, initialize a variable for time, and assign it millis()multiplied by a thousand. Refer back to the Timers lesson if you need a refresher on millis(). Next, have the function return the time plus 1 in percent form.

Finally, include the connection and takeoff in void setup.

#include <CoDrone.h>

int RandomNum(int x){
    int time = int(millis() * 1000);
    return time % (x + 1);
  }
  
void setup(){
    CoDrone.begin(115200); 
    CoDrone.pair();
    CoDrone.takeoff();
}

In void loop, set pin 11 as a sensor. Write your program so that if IR sensor 11 is triggered, your CoDrone will stop. Else, your CoDrone will yaw to the right with the arms flickering a random color.

Wondering why there’s three RandomNum return functions in a row? You want a random value to be returned for the R, G, and B values of the LED.

void loop() {
  
  byte bt1 = digitalRead(11);

  if (bt1) {
     CoDrone.emergencyStop();
  
  }
  else if (!bt1){
    CoDrone.setYaw(50);
    CoDrone.setArmLED(RandomNum(255),RandomNum(255),RandomNum(255), BLINK, 50);
  }
}

Your final code should look like this:

#include <CoDrone.h>

  int RandomNum(int x){
  int time = int(millis() * 1000);
  return time % (x + 1);
  }
  
void setup(){
  CoDrone.begin(115200); 
  CoDrone.pair();

  CoDrone.takeoff();
}

void loop() {
  
  byte bt1 = digitalRead(11);

  if (bt1) {
     CoDrone.emergencyStop();
  
  }
  else if (!bt1){
    CoDrone.setYaw(50);
    CoDrone.setArmLED(RandomNum(255),RandomNum(255),RandomNum(255), BLINK, 50);
  }
}

Challenge: Wandering CoDrone

Create a program that will make your CoDrone fly in random directions at random speeds!

Rules:

1. Make sure your location has a lot of room to fly in multiple directions.
2. Use return functions to return your random numbers.
3. Do not go up to 100 on your throttle!
4. Make sure you include a kill switch!