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2. Add a button

2.2. if...else statements

// check if the pushbutton is pressed. If it is, the buttonState is HIGH:
  if (buttonState == HIGH) {
    // turn LED on:
    digitalWrite(ledPin, HIGH);
  } else {
    // turn LED off:
    digitalWrite(ledPin, LOW);
  }

Inside the loop() function we have what is called a conditional statement. Conditional statements in programming allow something to happen/executed if a condition is met. 

Some conditional statements in real life:

  • If the birds are flying low, it is going to rain.
  • If you turn on the radio, it will play music.
  • If the light is red, the cars stop. 
The general structure of an if...else statement in C goes like this:

  if (some_condition) {
    // execute the following if the condition is TRUE
    do_this;
    and_this;
 } else {
   // execute the following if the condition is FALSE 
   do_that;
  }

In the Button sketch, the if statement checks to see if buttonState is HIGH. If the condition is met, the 

    digitalWrite(ledPin, HIGH);
command is executed. If not, the code contained inside the else is executed instead: 
    digitalWrite(ledPin, LOW);
. If statements can exist alone, or with one or more else statements.


One important thing to note is that 

==
is a comparison operator, not the same as 
=
, which is an assignment operator.

Inside the if statement condition, only the following and their combinations can be used:

x == y (x is equal to y)
x != y (x is not equal to y)
x <  y (x is less than y)
x >  y (x is greater than y)
x <= y (x is less than or equal to y)
x >= y (x is greater than or equal to y)

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