Adjust Initialization, Condition, and Increment

As mentioned earlier, i++ uses the ++ increment operator to add 1 to the i variable each time through the for loop.  There are also compound operators for decrement --, and compound arithmetic operators like +=, -=, *=, and /=.  For example, the += operator can be used to write i = i + 1000 like this: i+=1000. 

  • Save your sketch, then save it as CountHigherInSteps.
  • Replace the for statement in the sketch with this:
for(int i = 5000; i <= 15000; i+=1000)
  • Upload the modified sketch and watch the output in the Serial Monitor.

 

A Loop that Repeats While a Condition is True

In later chapters, you’ll use a while loop to keep repeating things while a sensor returns a certain value.  We don’t have any sensors connected right now, so let’s just try counting to ten with a while loop:

int i = 0;
  while(i < 10)
  {
    i = i + 1;  
    Serial.println(i);
    delay(500);
  }

Want to condense your code a little?  You can use the increment operator (++) to increase the value of i inside the Serial.println statement.  Notice that ++ is on the left side of the i variable in the example below.  When ++ is on the left of a variable, it adds 1 to the value of i before the println function executes.  If you put ++ to the right, it would add 1 after println executes, so the display would start at zero.

 int i = 0;
  while(i < 10)
  {
    Serial.println(++i);
    delay(500);
  }

The loop function, which must be in every Arduino sketch, repeats indefinitely.  Another way to make a block of statements repeat indefinitely in a loop is like this:

 int i = 0;
  while(true)
  {
    Serial.println(++i);
    delay(500);
 }

So why does this work?  A while loop keeps repeating as long as what is in its parentheses evaluates as true.  The word 'true' is actually a pre-defined constant, so while(true) is always true, and will keep the while loop looping.  Can you guess what while(false) would do?

  • Try these three different while loops in place of the for loop in the CountToTen sketch. 
  • Also try one instance using Serial.println(++i), and watch what happens in the Serial Monitor.
  • Try while(true) and while(false) also.