Page 62 - Programming the Photon Getting Started With the Internet of Things

Commands

The C language on the Photon has a number of built-in commands. In this section we will
explore some of these commands and see how they can be used in our firmware.

The if Statement

In our examples so far we have assumed that your lines of programming will be executed
in order one after the other. But what if we don’t want to do this and we want to execute a
block of code when something happens in the code. For this we can use an if statement,

which is used in conjunction with a comparison operator, and test whether a certain
condition has been reached, such as an input being higher or lower than a certain number.
The formatting for an if statement is as follows:

if (variable > 50)

{
//Write your code here
}

The program tests to see if the variable is greater than 50. If it is, then the program
takes a particular action and executes the code in between the curly braces. If the
condition is not reached, then the program skips over this section and moves on to the
next. Also, the curly braces may be omitted after an if statement; if this is done, then the

next line of code becomes the only conditional statement, as shown in the next example:

if (x > 50) digitalWrite(LEDpin, HIGH);
if (x > 50)
digitalWrite(LEDpin, HIGH);
if (x > 50) { digitalWrite(LEDpin, HIGH); }

if (x > 50) {
digitalWrite(ledPin1, HIGH);
digitalWrite(ledPin2, HIGH);
}

All of the examples are correct for using an if statement. Note that we used the
symbol >, which means “more than.” It is one example of what are called comparison
operators. These operators can be found in Table 3.2.