Combining Conditions

Part of the First Circuits section of Coddy's Arduino journey. Lesson 21 of 22.

Two conditions can be joined into one:

&& means and: true only when both sides are true
|| means or: true when at least one side is true

if (count >= 3 && count <= 7) { ... }   // 3, 4, 5, 6 or 7
if (count == 1 || count == 9) { ... }   // 1 or 9

The first reads "count is at least 3 and at most 7": a range. The second reads "count is 1 or count is 9".

Each side must be a whole comparison. count == 1 || 9 does not mean "1 or 9": the right side is 9 on its own, which the board treats as true, so the whole condition is always true.

And count >= 3 || count <= 7 is always true too, because every number is either at least 3 or at most 7. A range needs &&.

Challenge

Medium

The starter counts up every 300 ms. Red LED on pin 8, green LED on pin 9. Each time round:

turn green on when count is from 4 to 6 (4, 5 or 6), and off otherwise
turn red on when count is 2 or 8, and off otherwise

Press Run, then Check.

Try it yourself

int count = 0;

void setup() {
  pinMode(8, OUTPUT);  // red
  pinMode(9, OUTPUT);  // green
  Serial.begin(9600);
}

void loop() {
  count = count + 1;
  Serial.println(count);
  // green on from 4 to 6, red on at 2 and at 8
  delay(300);
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in First Circuits

1Hello, Board

Blink an LED Setup and Loop Change the Blink Speed An LED of Your Own Two LEDs Taking Turns Comments in Your Sketch

4Decisions

Decisions with if Choosing with if and else Comparing ValuesCombining ConditionsRead a Button

2Talking to Your Computer

Hello, Serial Monitor Print Versus Println Printing Numbers Your First Variable Counting Up When an Int Runs Out

3Math on the Board

Named Constants Arithmetic Operators Integer Division Decimals with float A Blink That Speeds Up

Practice on your own: Arduino playground