Functions in Dart

What is a Function?

A function is a reusable block of code that performs a specific task. Functions help you avoid code repetition, improve readability, and make your code easier to test and maintain.

Syntax

returnType functionName(parameters) {
  // function body
  return value;  // if returnType is not void
}

Return Types

int add(int a, int b) {
  return a + b;
}

double circleArea(double radius) {
  return 3.14159 * radius * radius;
}

String greet(String name) {
  return 'Hello, $name!';
}

bool isEven(int n) {
  return n % 2 == 0;
}

Void Functions

Functions that do not return a value use void as return type:

void printLine() {
  print('─' * 30);
}

void showInfo(String name, int age) {
  print('Name: $name, Age: $age');
}

Example

void main() {
  // Call functions
  int result = add(10, 20);
  print('Sum: $result');                   // 30

  double area = circleArea(7.0);
  print('Area: $${area.toStringAsFixed(2)}'); // 153.94

  print(greet('Dart'));                    // Hello, Dart!
  print(isEven(42));                       // true
  printLine();
  showInfo('Alice', 25);
}

int add(int a, int b) => a + b;

double circleArea(double r) => 3.14159 * r * r;

String greet(String name) => 'Hello, $name!';

bool isEven(int n) => n % 2 == 0;

void printLine() => print('─' * 30);

void showInfo(String name, int age) =>
    print('Name: $name, Age: $age');

Sum: 30
Area: 153.94
Hello, Dart!
true
──────────────────────────────
Name: Alice, Age: 25

🧠 Quiz

Summary

Functions in Dart are defined with a return type, name, parameters, and body. Use void for functions that return nothing. Functions can be defined at the top level or inside classes. They eliminate repetition and make code reusable.