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In Dart, a function is a block of code that performs a specific task, can take inputs, and may return a result. Functions help organize code, make it reusable, and improve readability. Dart functions are first-class objects, meaning they can be assigned to variables, passed as arguments, and returned from other functions. Functions in Dart support both named and positional parameters and offer optional parameters and default values.
Function Types
Function Types
In Dart, a function is a block of reusable code that performs a specific task.
Functions help organize code, make it more readable, and allow for reuse without rewriting the same code.
Dart supports different types of functions, including named functions, anonymous functions, and arrow functions.
1. Basic Syntax of a Function
1. Basic Syntax of a Function
returnType functionName(parameters) {
// function body
return value; // optional
}
returnType: The data type of the value the function returns. Use void if the function doesn’t return anything.
functionName: The name of the function.
parameters: The input values that the function takes (optional).
return: Returns a value from the function (optional).
Example of a Simple Function
Example of a Simple Function
Adds two numbers and returns the result:
Function-
int add(int a, int b) {
return a + b;
}
void main() {
int result53 = add(5, 3); // function calling
print("The result is: $result53");
int result32 = add(3,2); // function calling
print("The result is: $result32");
}
2. Void Functions
2. Void Functions
If a function doesn’t return any value, you can specify the return type as void.
Example:
void greet(String name) {
print("Hello, $name!");
}
void main() {
greet("Alice");
}
3. Optional Positional Parameters
3. Optional Positional Parameters
In Dart, you can make parameters optional by enclosing them in square brackets [].
Optional parameters have a default value of null unless you specify a default value.
Example:
void describe(String name, [int? age])
{
if (age != null) {
print("$name is $age years old.");
} else
{
print("Name is $name.");
}
}
void main() {
describe("Bob", 25);
describe("Alice"); // without passing age parameter
}
4. Named Parameters
4. Named Parameters
Named parameters allow you to specify which parameter to set when calling the function, making code more readable. Named parameters are enclosed in curly braces {}.
Example:
void displayInfo({String? name, int? age}) {
print("Name: $name, Age: $age");
}
void main() {
displayInfo(name: "John", age: 30);
displayInfo(age: 22, name: "Emma"); // order doesn't matter
}
5. Arrow Functions
5. Arrow Functions
Arrow functions are shorthand for functions that contain only one expression. They are defined using => instead of {}.
Example:
int multiply(int a, int b) => a * b;
void main() {
print(multiply(4, 5)); // Outputs: 20
}
6. Anonymous Functions (Lambdas)
6. Anonymous Functions (Lambdas)
An anonymous function is a function without a name. It’s often used as an argument in higher-order functions like forEach.
Example:
void main() {
List<int> numbers = [1, 2, 3, 4, 5];
numbers.forEach((number) {
print(number * 2);
});
}
7. Function with Default Parameter Values
7. Function with Default Parameter Values
You can also assign default values to parameters, which are used if no value is passed for that parameter.
Example:
void greet(String name, [String greeting = "Hello"]) {
print("$greeting, $name!");
}
void main() {
greet("Alice"); // Uses default greeting
greet("Bob", "Hi"); // Uses provided greeting
}
8. Higher-Order Functions
8. Higher-Order Functions
A higher-order function is a function that can take another function as a parameter or return a function.
Example:
void main() {
// Passing a function as a parameter
List<int> numbers = [1, 2, 3];
numbers.forEach(printDouble); // Calls printDouble for each number
}
void printDouble(int number) {
print(number * 2);
}
Basic Definition & calling
Basic Definition & calling
Defined outside of main()-
void main()
{
greet(); // Function call
}
void greet() // Function definition
{
print("Hello, welcome to Dart!");
}
Defined inside of main()-
void main() {
// Function definition
void greet() {
print("Hello, welcome to Dart!");
}
// Function call
greet();
}
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1. Function to Add Two Numbers
1. Function to Add Two Numbers
void main() {
int sum = add(5, 10);
print("Sum: $sum");
}
int add(int a, int b) {
return a + b;
}
2. Function to Check if a Number is Even or Odd
2. Function to Check if a Number is Even or Odd
void main() {
print(isEven(4)); // true
print(isEven(7)); // false
}
bool isEven(int number) {
return number % 2 == 0;
}
3. Function to Find the Factorial of a Number
3. Function to Find the Factorial of a Number
void main() {
print("Factorial of 5: ${factorial(5)}");
}
int factorial(int number) {
if (number <= 1) return 1;
return number * factorial(number - 1);
}
4. Function to Calculate the Area of a Circle
4. Function to Calculate the Area of a Circle
void main() {
print("Area of circle with radius 3: ${circleArea(3)}");
}
double circleArea(double radius) {
const double pi = 3.14159;
return pi * radius * radius;
}
5. Function to Check if a String is a Palindrome
5. Function to Check if a String is a Palindrome
void main() {
print(isPalindrome("madam")); // true
print(isPalindrome("hello")); // false
}
bool isPalindrome(String text) {
String reversed = text.split('').reversed.join('');
return text == reversed;
}
6. Function to Find the Maximum of Three Numbers
6. Function to Find the Maximum of Three Numbers
void main() {
print("Max of 10, 20, 15: ${maxOfThree(10, 20, 15)}");
}
int maxOfThree(int a, int b, int c) {
return (a > b && a > c) ? a : (b > c ? b : c);
}
7. Function to Convert Celsius to Fahrenheit
7. Function to Convert Celsius to Fahrenheit
void main() {
print("30°C in Fahrenheit: ${celsiusToFahrenheit(30)}");
}
double celsiusToFahrenheit(double celsius) {
return (celsius * 9 / 5) + 32;
}
8. Function to Print Fibonacci Sequence up to n Terms
8. Function to Print Fibonacci Sequence up to n Terms
void main() {
fibonacci(5); // 0 1 1 2 3
}
void fibonacci(int n) {
int a = 0, b = 1;
for (int i = 0; i < n; i++) {
print(a);
int temp = a;
a = b;
b = temp + b;
}
}
9. Function to Count Vowels in a String
9. Function to Count Vowels in a String
void main() {
print("Vowels in 'hello': ${countVowels("hello")}");
}
int countVowels(String str) {
int count = 0;
for (var char in str.toLowerCase().split('')) {
if ('aeiou'.contains(char)) {
count++;
}
}
return count;
}
10. Function to Find the GCD of Two Numbers
10. Function to Find the GCD of Two Numbers
void main() {
print("GCD of 48 and 18: ${gcd(48, 18)}");
}
int gcd(int a, int b) {
while (b != 0) {
int temp = b;
b = a % b;
a = temp;
}
return a;
}
Define outside
Define outside
void main()
{
greet(); // Function call
}
void greet() // Function definition
{
print("Hello, welcome to Dart!");
}
Ex=
void main()
{
display(); //calling
}
display()
{
print('defining outside'); //Defining
}
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1. Basic Function Syntax
1. Basic Function Syntax
A function in Dart is defined using the following syntax:
returnType functionName(parameters)
{
// Function body
return value;
}
returnType: Specifies the type of value returned by the function (e.g., int, String, void). If the function does not return anything, void is used.
functionName: The name of the function.
parameters: Input values that the function can take, separated by commas.
return: The keyword return sends a value back to where the function was called.
2. Example of a Simple Function
2. Example of a Simple Function
int add(int a, int b)//Defining function
{
return a + b;
}
void main() {
int sum = add(5, 3); //calling function
print("Sum: $sum"); // Output: Sum: 8
}
3. Arrow Functions (Short Syntax)
3. Arrow Functions (Short Syntax)
For simple functions with one expression, Dart allows using arrow syntax (=>) to define the function:
int multiply(int a, int b) => a * b; //Syntaxt:- returnType functionName(parameters) => return values;
void main() {
print(multiply(4, 5)); // Output: 20
}
4. Optional Parameters
4. Optional Parameters
Dart functions can have optional parameters, either positional or named.
Optional Positional Parameters
These are wrapped in square brackets []. If not provided, they are null by default unless a default value is specified.
void greet(String name, [String? message]) {
print("Hello $name! ${message ?? ''}");
}
void main() {
greet("Alice"); // Output: Hello Alice!
greet("Alice", "Welcome!"); // Output: Hello Alice! Welcome!
}
Optional Named Parameters
Named parameters are enclosed in curly braces {}. You can make them required using required, or assign default values.
void displayInfo(String name, {int age = 18, required String city}) {
print("$name, Age: $age, City: $city");
}
void main() {
displayInfo("Bob", city: "New York"); // Output: Bob, Age: 18, City: New York
}
5. Default Values
5. Default Values
Optional parameters can have default values, which are used if no argument is passed for that parameter.
void greet(String name, [String message = "Welcome!"]) {
print("Hello $name! $message");
}
void main() {
greet("Alice"); // Output: Hello Alice! Welcome!
}
6. Anonymous Functions (Lambda or Inline Functions)
6. Anonymous Functions (Lambda or Inline Functions)
Anonymous functions are functions without a name. They are often used as arguments to higher-order functions like map, forEach, etc.
void main() {
var numbers = [1, 2, 3];
numbers.forEach((num) {
print(num * 2); // Output: 2, 4, 6
});
}
7. Higher-Order Functions
7. Higher-Order Functions
Dart supports higher-order functions, meaning functions can take other functions as parameters or return functions.
void executeOperation(int a, int b, Function operation) {
print("Result: ${operation(a, b)}");
}
int add(int x, int y) => x + y;
void main() {
executeOperation(5, 3, add); // Output: Result: 8
}
8. Closures
8. Closures
A closure is a function that captures variables from its surrounding scope. This allows the function to use and modify variables even after the outer function has finished executing.
Function createCounter() {
int count = 0;
return () {
count += 1;
return count;
};
}
void main() {
var counter = createCounter();
print(counter()); // Output: 1
print(counter()); // Output: 2
}
9. Recursive Functions
9. Recursive Functions
A recursive function is one that calls itself, often used to solve problems that can be broken down into smaller, similar sub-problems.
int factorial(int n) {
if (n <= 1) return 1;
return n * factorial(n - 1);
}
void main() {
print(factorial(5)); // Output: 120
}
10. Using void for No Return Type
10. Using void for No Return Type
If a function doesn’t return any value, it can be defined with a void return type.
void greet() {
print("Hello, World!");
}
void main() {
greet(); // Output: Hello, World!
}
Define Inside
Define Inside
void main()
{
// Function definition
void greet() {
print("Hello, welcome to Dart!");
}
// Function call
greet();
}
Ex=
void main()
{
void display() // Defining
{
print('Function define inside'); //defined than calling
}
display(); //calling
}
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1. Add Two Numbers
1. Add Two Numbers
void main()
{
int add(int a, int b){
return a+b;
}
print('Sum= ${add(2,3)}');
print('Sum 3,4= ${add(5,8)}');
}
2. Check if a Number is Even or Odd
2. Check if a Number is Even or Odd
void main() {
bool isEven(int number) {
return number % 2 == 0;
}
print(isEven(7) ? "Even" : "Odd"); //Calling & Output: Odd
}
3. Calculate Factorial of a Number
3. Calculate Factorial of a Number
void main()
{
int factorial(int n){
if (n<=1) return 1;
return n*factorial(n-1);
}
print('Factorial of 3: ${factorial(3)}');
print('Factorial of -2: ${factorial(-2)}');
}
4. Check if a String is a Palindrome
4. Check if a String is a Palindrome
void main() {
bool isPalindrome(String str) {
return str == str.split('').reversed.join('');
}
print(isPalindrome("radar")); // Output: true
print(isPalindrome("hello")); // Output: false
}
5. Find Maximum of Three Numbers
5. Find Maximum of Three Numbers
void main()
{
int maxOfThree(int a, int b, int c){
return (a>b && a>c)?a:(b>c?b:c);
}
print('Maxof1,9,5: ${maxOfThree(1, 9, 5)}');
print('Maxof-1,7,5: ${maxOfThree(-1, 7, 5)}');
print('Maxof1,1,0: ${maxOfThree(1, 1, 0)}');
}
6. Convert Celsius to Fahrenheit
6. Convert Celsius to Fahrenheit
void main() {
double celsiusToFahrenheit(double celsius) {
return (celsius * 9 / 5) + 32;
}
print("30°C in Fahrenheit: ${celsiusToFahrenheit(30)}"); // Output: 86.0
}
7. Count Vowels in a String
7. Count Vowels in a String
void main() {
int countVowels(String str) {
int count = 0;
for (var char in str.toLowerCase().split('')) {
if ('aeiou'.contains(char)) {
count++;
}
}
return count;
}
print("Vowels in 'hello': ${countVowels("hello")}"); // Output: 2
}
8. Check if a Number is Prime
8. Check if a Number is Prime
void main() {
bool isPrime(int n) {
if (n <= 1) return false;
for (int i = 2; i <= n ~/ 2; i++) {
if (n % i == 0) return false;
}
return true;
}
print("Is 7 prime? ${isPrime(7)}"); // Output: true
print("Is 10 prime? ${isPrime(10)}"); // Output: false
}
9. Print Fibonacci Sequence up to n Terms
9. Print Fibonacci Sequence up to n Terms
void main() {
void fibonacci(int n) {
int a = 0, b = 1;
for (int i = 0; i < n; i++) {
print(a);
int temp = a;
a = b;
b = temp + b;
}
}
fibonacci(5); // Output: 0 1 1 2 3
}
10. Calculate Area of a Circle
10. Calculate Area of a Circle
void main() {
double circleArea(double radius) {
const double pi = 3.14159;
return pi * radius * radius;
}
print("Area of circle with radius 3: ${circleArea(3)}"); // Output: 28.27431
}
with Parameters
with Parameters
Functions can accept parameters to work with different inputs.
void main()
{
display('Sandeep');
display('Pradeep');
}
void display(String name)
{
print('Name is: $name');
}
Ex=
void main() {
// Function that takes a name and prints a personalized message
void greet(String name) // name as parameter
{
print("Hello, $name! Welcome to Dart!");
}
// Calling the function with an argument
greet("Alice"); // calling with parameter
greet("Bob");
}
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Functions With Parameters
Functions With Parameters
1. Add Two Numbers
void main() {
int sum = add(5, 10);
print("Sum: $sum");
}
int add(int a, int b) {
return a + b;
}
2. Calculate Area of a Circle
void main() {
double areaOfCircle(double radius) {
const double pi = 3.14159;
return pi * radius * radius;
}
print("Area of circle: ${areaOfCircle(4)}"); // Output: 50.26544
}
3. Convert Celsius to Fahrenheit
void main() {
double celsiusToFahrenheit(double celsius) {
return (celsius * 9 / 5) + 32;
}
print("30°C in Fahrenheit: ${celsiusToFahrenheit(30)}"); // Output: 86.0
}
4. Check if a Number is Even or Odd
void main() {
bool isEven(int number) {
return number % 2 == 0;
}
print(isEven(4) ? "Even" : "Odd"); // Output: Even
print(isEven(7) ? "Even" : "Odd"); // Output: Odd
}
5. Find Maximum of Three Numbers
void main() {
int maxOfThree(int a, int b, int c) {
return (a > b && a > c) ? a : (b > c ? b : c);
}
print("Max: ${maxOfThree(5, 10, 8)}"); // Output: Max: 10
}
Functions Without Parameters
Functions Without Parameters
6. Print a Greeting Message
void main() {
void greet() {
print("Hello, welcome to Dart programming!");
}
greet(); // Output: Hello, welcome to Dart programming!
}
7. Print the Current Date and Time
void main() {
void printCurrentDateTime() {
DateTime now = DateTime.now();
print("Current Date and Time: $now");
}
printCurrentDateTime(); // Output: Current Date and Time: [current date and time]
}
8. Print First 10 Fibonacci Numbers
void main() {
void printFibonacci() {
int a = 0, b = 1;
for (int i = 0; i < 10; i++) {
print(a);
int temp = a;
a = b;
b = temp + b;
}
}
printFibonacci(); // Output: First 10 Fibonacci numbers
}
9. Display a Simple Message
void main() {
void showMessage() {
print("This is a simple message without any parameters.");
}
showMessage(); // Output: This is a simple message without any parameters.
}
10. Print Numbers from 1 to 5
void main() {
void printNumbers() {
for (int i = 1; i <= 5; i++) {
print(i);
}
}
printNumbers(); // Output: 1 2 3 4 5
}
with return value
with return value
Functions can return values to the caller using the return keyword.
void main() {
// Function that calculates the square of a number
int square(int num)
{
return num * num;//function returning
}
// Calling the function and printing the result
int result = square(4);
print("The square of 4 is: $result");
}
Ex=
void main() {
// Function that calculates the square of a number
int square(int num) {
int square = num * num;
return square; //function returning
}
// Calling the function and printing the result
int fourSq = square(4);
print("The square of 4 is: $fourSq");
}
Functions With Return Values
Functions With Return Values
A function with a return value sends back a result to where it was called using the return keyword.
(Same to above examples)
1. Add Two Numbers and Return the Sum
void main() {
int add(int a, int b) {
return a + b;
}
int result = add(5, 3);
print("Sum: $result"); // Output: Sum: 8
}
2. Calculate and Return Area of a Circle
void main() {
double areaOfCircle(double radius) {
const double pi = 3.14159;
return pi * radius * radius;
}
double area = areaOfCircle(4);
print("Area of circle: $area"); // Output: Area of circle: 50.26544
}
3. Convert Celsius to Fahrenheit and Return the Result
void main() {
double celsiusToFahrenheit(double celsius) {
return (celsius * 9 / 5) + 32;
}
double fahrenheit = celsiusToFahrenheit(30);
print("30°C in Fahrenheit: $fahrenheit"); // Output: 86.0
}
4. Find and Return the Maximum of Three Numbers
void main() {
int maxOfThree(int a, int b, int c) {
return (a > b && a > c) ? a : (b > c ? b : c);
}
int max = maxOfThree(5, 10, 8);
print("Max: $max"); // Output: Max: 10
}
5. Calculate and Return the Factorial of a Number
void main() {
int factorial(int n) {
if (n <= 1) return 1;
return n * factorial(n - 1);
}
int result = factorial(5);
print("Factorial of 5: $result"); // Output: 120
}
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