For Loops

Step 1

What are for loops?

For loops are a lot like while loops — they repeat lines of code while a condition is true. However, the condition is a specific number of times that you set. For example, if you only wanted your line of code to repeat 87 times, you would use a for loop.

The conditional statement for a for loop follows a very specific format that looks intimidating, but we’ll break it down!

for(initialization; condition; increment){ 
    statement;
}

This is what all of that means:

Initialization is where you establish the private variable, which is usually just an integer, that your for loop will start from. Private variables can only be used within a limited scope, so in this case, the private variable can only be used in the for loop.
Condition is what has to be true in order for the for loop to repeat. This has to use the private variable that’s in initialization!
Increment is how much the private variable will be increased or decreased for each loop.
Statement is the section of code that’s read for each loop.

Example time!

If you want to make a square, you would need your code to repeat four times. A for loop would be perfect for this task! Look at that code below to see exactly how you would use it.

for(int i = 1; i < 4; i++){
    CoDrone.setPitch(50);
    CoDrone.setYaw(50);
    CoDrone.move();
}

This is the pseudocode:

Start i at 1.
If i is less than 4, pitch forward at 50 and yaw right at 50.
Add 1 to i.
Repeat until i is greater than 4,

Step 2

For loop example

Try this for loop program and open your serial monitor to see what happens!

void setup() {
    Serial.begin(9600);
}

void loop() { 
    for ( int i = 0; i < 5 ; i++ ) {
    Serial.print("hello");
    }
    Serial.println();
}

Check out the conditional statement to see what’s going on:

int i = 0 Private variable i is an integer that starts out with a value of 0.
i < 5 As long as i is less than 5, the loop will continue.
i++ At the end of each loop, the value of i is increased by 1.

Important to know: once i is greater than 5, the statement is no longer true so the loop will not execute.

Step 3

Bouncing LEDs

Let’s bring the for loop to your CoDrone’s remote control. Use this code to make your remote’s LED look like it’s bouncing from side to side!

void setup() {
    pinMode(11, OUTPUT);
    pinMode(12, OUTPUT);
    pinMode(13, OUTPUT);
    pinMode(14, OUTPUT);
    pinMode(15, OUTPUT);
    pinMode(16, OUTPUT);
    pinMode(17, OUTPUT);
    pinMode(18, OUTPUT);
}
void loop() {
    LEDBounce();
} void LEDBounce() {
    for ( int i = 11; i <= 18; i++) {
        digitalWrite(11, LOW);
        digitalWrite(12, LOW);
        digitalWrite(13, LOW);
        digitalWrite(14, LOW);
        digitalWrite(15, LOW);
        digitalWrite(16, LOW);
        digitalWrite(17, LOW);
        digitalWrite(18, LOW);
        digitalWrite(i, HIGH);
        delay(200);
    }
    for ( int i = 18; i >= 11; i--) {
        digitalWrite(11, LOW);
        digitalWrite(12, LOW);
        digitalWrite(13, LOW);
        digitalWrite(14, LOW);
        digitalWrite(15, LOW);
        digitalWrite(16, LOW);
        digitalWrite(17, LOW);
        digitalWrite(18, LOW);
        digitalWrite(i, HIGH);
        delay(200);
    }
}

This is the pseudocode:

Set up pins 11 through 18 as outputs.
Start i’s value as 11 and as long as i is less than or equal to 18, add 1 to i.
If i’s value is between 11 and 18, turn its corresponding LED on for 2 seconds.
Start i’s value as 18 and as long as i is greater than or equal to 11, subtract 1 from i.
If i’s value is between 11 and 18, turn its corresponding LED on for 2 seconds.

Step 4

Flying circles with for loops

You can use for loops to program your CoDrone to fly in a circle!…kind of. The problem is that computers think in coordinates, lines, and angles, so they usually aren’t great at round edges. This is perfect for angular shapes like squares and rectangles, but bad for things like circles, ovals, and figure eights.

So. What can you do?

Instead of programming a perfect round circle, you’re going to program your CoDrone to fly in a shape that closely imitates a circle. One of the best shapes to start with is an octagon! You can have your drone constantly pitch and roll in diagonals until it’s back where it started.

Step 5

Make a tetracontagon

Octagons are great, but if you add even more sides to it, your CoDrone will fly in a pattern that looks more like a circle. Try having your CoDrone fly in a tetracontagon, which is a 40 sided polygon! If you don’t want to set the individual pitch and roll for all 40 sides, use a for loop instead. This is what that statement would look like:

for (int i = 0; i < 40 ; i++)

Step 6

Circle code

Try this code out so your CoDrone can fly in a circle! This segment of the code would go into void loop.

void Circle() {
    int Roll = 55;
    int Pitch = 0; 
    for (int i = 0; i < 40 ; i++) { 
        if (i < 10) {
            Pitch = Pitch + 5;
            Roll = Roll - 5;
        }
        else if (i < 20) {
            Pitch = Pitch - 5;
            Roll = Roll - 5;
        }
        else if (i < 30) {
            Pitch = Pitch - 5;
            Roll = Roll + 5;
        }
        else {
            Pitch = Pitch + 5;
            Roll = Roll + 5;
        }
        CoDrone.setPitch(Pitch);
        CoDrone.setRoll(Roll);
        CoDrone.move(0.1);
    }
}

Some things you need to know:

The Circle() function uses a for loop to split the circle into 40 sides.
For the first 10 sides of the circle, add increments of 5 to pitch, but subtract increments of 5 from roll.
For sides 11-20, start subtracting increments of 5 from pitch and roll in a new else if statement.
For sides 21-30, keep subtracting increments of 5 from pitch but add increments of 5 to roll in another else if statement.
For sides 31-40, add increments of 5 to both pitch and roll in an else statement.
The length of delay() at the end will determine how long each side of your circle is. For a circle with a large diameter, use longer delays!

Tetracontagon for loop with pitch and roll

Step 7

Fake for loops

One potential downside of a for loop is that it prevents the rest of your code from looping until the entire for loop is completed. This may be exactly what you want, but if, for example, you needed to use a kill switch, you would need to wait until the for loop is finished.

One way around this problem is to create an if statement that acts like a for loop. We know, we know, it seems like we taught you for loops for no reason! However, this will help you out if you need to have more options in your program.

Try this for loop out in your serial monitor. Notice how it goes through the entire loop before printing “hi”? Look at the image below to see what the output looks like if you can’t see it in your serial monitor!

void setup() {
    Serial.begin(9600);
}
void loop() {
    Test();
    Serial.println("hi");
    delay(1000); //wait 1000 milliseconds or 1 second
}
 
void Test() {
    for ( int i = 0; i < 10; i++) {
        Serial.print(i);
    }
    Serial.println();
}

Step 8

Interrupt your loop

If you want to be able to interrupt your loop, you can replace it with if (and else if and else) statements instead. Just make sure that you keep the condition in your if statement.

void setup() {
    Serial.begin(9600);
} 
void loop() {
    Test();
    Serial.println("hi");
    delay(1000); //wait 1000 milliseconds or 1 second
}
 
void Test() {
    static int i = 0;
    if ( i < 10) {
        Serial.print(i);
        i++;
    }
    else {
        i = 0;
        Serial.println();
    }
}

Wondering why i has static before it? This will make sure that i’s value won’t be overwritten every time the function void Test() is run.

Step 9

Challenge

Challenge: Figure Eight

Use for loops (fake or real) to have your CoDrone fly in a figure eight!

Rules

Your figure eight must have curves. It cannot look like a digital figure eight with angles!
You must use for loops (fake or real) to do this!
Don’t forget to include a kill switch!

This lesson works with:

Grade level:

Approx. time required:

CSTA

CCSS