Lesson 3: Calculations with Variables

What should you remember from Lesson 2?

Lesson 2 already introduced variables and some basic types. In this lesson, we will use those ideas instead of starting over from the beginning.

Most useful types for now

Small review example

// Integer examples
int temperature = 25;           // Room temperature
byte ledBrightness = 128;       // LED brightness (0-255)

// Decimal examples
float voltage = 3.3;            // Precise voltage reading

// Boolean examples
bool ledState = true;           // LED is on
bool buttonPressed = false;     // Button is not pressed

// Character and String examples
char grade = 'A';               // Single letter grade
String message = "Hello, World!";  // Text message

// A constant
const int maxScore = 10;

Variable Declaration and Initialization

Variables are containers that store data values. You need to declare them before use and can initialize them with starting values.

// Basic syntax: dataType variableName = initialValue;

// Declaration only (value is undefined)
int counter;
float temperature;
bool isRunning;

// Declaration with initialization (recommended)
int ledPin = 13;                    // Pin number for LED
float sensorVoltage = 0.0;          // Starting voltage
bool systemReady = false;           // System status
String deviceName = "Arduino";      // Device identifier

// Multiple variables of same type
int redPin = 9, greenPin = 10, bluePin = 11;
float x = 0.0, y = 0.0, z = 0.0;

// Constants (values that never change)
const int BUTTON_PIN = 2;           // Pin number (won't change)
const float MAX_VOLTAGE = 5.0;      // Maximum voltage
const String DEVICE_ID = "ROBOT_001";  // Device identifier

Variable Naming Best Practices

Basic Arithmetic Operators

Arduino supports all standard mathematical operations. Understanding these is essential for calculations involving counters, conversions, timing, and control logic.

// Mathematical operations examples
int a = 10;
int b = 3;
int result;

// Basic arithmetic
result = a + b;        // result = 13
result = a - b;        // result = 7
result = a * b;        // result = 30
result = a / b;        // result = 3 (integer division!)
result = a % b;        // result = 1 (remainder)

// Assignment operators
int counter = 0;
counter += 5;          // counter = 5 (same as counter = counter + 5)
counter -= 2;          // counter = 3
counter *= 4;          // counter = 12
counter /= 3;          // counter = 4

// Increment and decrement
counter++;             // counter = 5 (add 1)
counter--;             // counter = 4 (subtract 1)

// Working with floats for precise division
float voltage = 3.3;
float current = 0.02;
float resistance = voltage / current;  // resistance = 165.0

// Converting between types
int sensorValue = 512;
float percentage = (float)sensorValue / 1023.0 * 100.0;  // Convert to percentage

Practical Math Examples

void setup() {
  Serial.begin(9600);
  Serial.println("=== Variable Math Demo ===");

  // Example 1: Temperature conversion
  float celsius = 25.0;
  float fahrenheit = (celsius * 9.0 / 5.0) + 32.0;
  Serial.print(celsius);
  Serial.print(" C = ");
  Serial.print(fahrenheit);
  Serial.println(" F");

  // Example 2: Percentage calculation
  int score = 8;
  int total = 10;
  float percentage = (score / 10.0) * 100.0;
  Serial.print("Score: ");
  Serial.print(score);
  Serial.print("/");
  Serial.print(total);
  Serial.print(" = ");
  Serial.print(percentage);
  Serial.println("%");
}

void loop() {
}

Activity Instructions