if Test

The “if” is a test you give to the Arduino. In this test you make the questions and you determine what happens when it passes or fails. If the test that you made is passed, as in something happens that you wanted to happen, then you want the Arduino to do a certain action. Optionally, if the test is failed or something unexpected happens and the test is failed, you can tell the Arduino to take a different action.

If you wanted to make a test on the Arduino that would turn on a light for 5 seconds every time someone walked through a door it would look something like this:

if (PersonWalkingThroughDoor == 1) {
 digitalWrite(LIGHT, HIGH);
 delay(5000);
 digitalWrite(LIGHT, LOW);
 }

And a translated human readable version to understand whats going on:

if (a person walks through the door) {
 turn on the light;
 wait 5 seconds;
 turn off the light;
 }

Now, let’s try to understand the Arduino version of the test and see why it works…

A person can only be walking through the door or not, we can represent this as 1 or 0, respectively. Then, we can assign this state to a certain variable – which can be thought of as a digital box that can hold thing – we’ll call this variable “PersonWalkingThroughDoor”.

If a person is walking though a door our variable PersonWalkingThroughDoor would equal 1, otherwise it would be 0. Given this basic setup we can run a test, and that is exactly what this part of our code does:

if (PersonWalkingThroughDoor == 1) {

If our variable PersonWalkingThroughDoor is equal to 1, then it would pass our test and go into the action phase, where it would preform a certain task.

digitalWrite(LIGHT, HIGH);
delay(5000);
digitalWrite(LIGHT, LOW);
}

What happens in our “action phase” are just some basic commands, first we use digitalWrite() to set the pin attached to the LIGHT variable to HIGH (turning on the light), then we wait 5000 milliseconds, then we turn the light off.
Finally, if you want to expand the function of the test then you can include an “else” clause which would look something like this:


 if (PersonWalkingThroughDoor == 1) {
 digitalWrite(LIGHT, HIGH);
 delay(5000);
 digitalWrite(LIGHT, LOW);
 }
 else {digitalWrite(LIGHT, LOW);}

In that case, if the initial test is failed you can tell the Arduino to take a different action. In our case it would simply keep the light off if there is nobody walking through the door, and it truly inessential as the light is turned off by default after 5 seconds.

So that’s it, that’s the basic overview of an if function. You might know it, but the best way to understand it is to try it out yourself.

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