Control Structures (if, else)

Okay, here's an explanation of if and else control structures in Arduino, using plain English and examples.

Control Structures: if and else

if and else are fundamental building blocks in Arduino programming (and most programming languages) that allow your code to make decisions based on certain conditions. They control which blocks of code are executed.

1. The if Statement

The if statement checks whether a condition is true. If the condition is true, the code inside the curly braces {} following the if statement is executed. If the condition is false, that code is skipped.

• Syntax:

  if (condition) {
    // Code to be executed if the condition is true
  }
  

• Example:

  int sensorValue = 500; // Pretend this is a value read from a sensor
  
  void setup() {
    Serial.begin(9600); // Initialize serial communication for printing to the Serial Monitor
  }
  
  void loop() {
    if (sensorValue > 400) {
      Serial.println("Sensor value is high!");
    }
  
    delay(1000); // Wait for 1 second
  }
  

  In this example:

  • We have a variable sensorValue that holds a value.
  • The if statement checks if sensorValue is greater than 400.
  • Because sensorValue is 500, the condition sensorValue > 400 is true.
  • Therefore, the code Serial.println("Sensor value is high!"); will be executed, printing the message to the Serial Monitor.
  • If sensorValue was, say, 300, the message would not be printed.

2. The else Statement

The else statement is used in conjunction with an if statement. It provides an alternative block of code to execute when the if statement's condition is false.

• Syntax:

  if (condition) {
    // Code to be executed if the condition is true
  } else {
    // Code to be executed if the condition is false
  }
  

• Example:

  int sensorValue = 300;
  
  void setup() {
    Serial.begin(9600);
  }
  
  void loop() {
    if (sensorValue > 400) {
      Serial.println("Sensor value is high!");
    } else {
      Serial.println("Sensor value is low!");
    }
  
    delay(1000);
  }
  

  In this example:

  • sensorValue is 300.
  • The if statement checks if sensorValue is greater than 400. This is false.
  • Because the condition is false, the code inside the else block is executed: Serial.println("Sensor value is low!");
  • The Serial Monitor will show "Sensor value is low!".
  • If sensorValue was 500, the "Sensor value is high!" message would be printed, and the else block would be skipped.

3. else if Statements

You can chain multiple conditions together using else if. This allows you to check several conditions in sequence.

• Syntax:

  if (condition1) {
    // Code to be executed if condition1 is true
  } else if (condition2) {
    // Code to be executed if condition1 is false AND condition2 is true
  } else {
    // Code to be executed if both condition1 and condition2 are false
  }
  

• Example:

  int temperature = 25; // Temperature in Celsius
  
  void setup() {
    Serial.begin(9600);
  }
  
  void loop() {
    if (temperature > 30) {
      Serial.println("It's hot!");
    } else if (temperature > 20) {
      Serial.println("It's warm.");
    } else {
      Serial.println("It's cool.");
    }
  
    delay(1000);
  }
  

  In this example:

  • temperature is 25.
  • The first if statement (temperature > 30) is false.
  • The else if statement (temperature > 20) is true (because 25 is greater than 20).
  • Therefore, the message "It's warm." is printed.
  • The else block is skipped because one of the earlier conditions was met.

Important Notes:

• Conditions: The condition inside the parentheses () of an if or else if statement must evaluate to a boolean value: either true or false. You can use comparison operators (e.g., == (equal to), != (not equal to), > (greater than), < (less than), >= (greater than or equal to), <= (less than or equal to)) and logical operators (e.g., && (AND), || (OR), ! (NOT)) to create more complex conditions.
• Curly Braces: The curly braces {} define the block of code that belongs to the if, else if, or else statement. If you have only a single line of code to execute, you can omit the curly braces, but it's generally good practice to always use them for clarity and to avoid errors if you later add more code.

In short, if, else, and else if statements are essential for creating Arduino programs that react differently based on different inputs or conditions. They allow your Arduino to make decisions and control its behavior.