Parameters

In Dart programming, parameters are used to pass data into functions or constructors. Dart supports different types of parameters to provide flexibility when defining and calling functions. Let's explore them with examples:

Types of Parameters in Dart

1. Positional Parameters

• These parameters are mandatory and must be passed in the correct order.

Example:

void intro(String name, int age){

 print('My name is $name & age is $age');

}

void main()

{

 intro('Sandeep', 33);

}

2. Optional Positional Parameters

• Enclosed in square brackets [].

• If not provided, they default to null.

Example:

void intro(String name, [int? age])

{

 if(age!=null) {

   print('Hello, $name! You are $age years old');

 }

 else {

   print('Name is $name');

 }

}

void main()

{

 intro('Sam',23);

 intro('san');

}

3. Named Parameters

• Enclosed in curly braces {}.

• Can be passed in any order.

Example:

void intro({required String name, required int age})

{

 print('Hi! My name is $name & age is $age');

}

void main()

{

 intro(name: "Sandewep", age: 45);

 //intro(name: 'San'); Error

 intro(age: 78, name: "san");

}

4. Optional Named Parameters with Default Values

• Use {} and assign default values to the parameters.

Example:

void intro({ String name="Guest", int age=23})

{

 print('Hi! My name is $name & age is $age');

}

void main()

{

 intro();

 intro(name: "Sandewep", age: 45);

 intro(name: 'San');

 intro(age: 78, name: "san");

}

5. Required Named Parameters

• Use the required keyword to ensure the parameter must be provided.

Example:

void greet({required String name, required int age}) {

 print('Hello, $name! You are $age years old.');

}

void main() {

 greet(name: 'Alice', age: 25); // Output: Hello, Alice! You are 25 years old.

}

Note: Omitting a required parameter will result in a compile-time error.

6. Function with a Mix of Parameters

• Functions can combine positional, optional positional, and named parameters.

Example:

void describe(String name, [int? age], {String country = 'Unknown'}) {

 print('Name: $name, Age: ${age ?? 'Unknown'}, Country: $country');

}

void main() {

 describe('Alice', 25, country: 'USA'); // Output: Name: Alice, Age: 25, Country: USA

 describe('Bob');                       // Output: Name: Bob, Age: Unknown, Country: Unknown

}

7. Default Parameter Values

• Provide default values for optional parameters to avoid null checks.

Example:

void greet(String name, [String title = 'Guest']) {

 print('Hello, $title $name!');

}

void main() {

 greet('Alice');             // Output: Hello, Guest Alice!

 greet('Alice', 'Dr.');      // Output: Hello, Dr. Alice!

}

8. Passing a Function as a Parameter

• Functions can be passed as parameters to other functions.

Example:

void main() {

 // Calling the function with different parameter combinations

 calculateTotal(100, 5, discount: 10, tax: 8); // Example with all parameters

 calculateTotal(200, 3, discount: 20);        // Example without tax

 calculateTotal(150, 4);                      // Example with only required parameters

}

// Function with a mix of parameters

void calculateTotal(

   double price,

   int quantity,

   {double discount = 0, double tax = 0}) {

 // Calculate subtotal

 double subtotal = price * quantity;

 // Apply discount and tax

 double discountedPrice = subtotal - (subtotal * (discount / 100));

 double totalPrice = discountedPrice + (discountedPrice * (tax / 100));

 // Print the result

 print('Subtotal: \$${subtotal.toStringAsFixed(2)}');

 print('Discount: ${discount.toStringAsFixed(1)}%');

 print('Tax: ${tax.toStringAsFixed(1)}%');

 print('Total Price: \$${totalPrice.toStringAsFixed(2)}');

}

9. Parameters in Class Constructors

Example with Named and Positional Parameters:

class Person {

 String name;

 int age;

 Person(this.name, {required this.age});

 void display() => print('Name: $name, Age: $age');

}

void main() {

 var person = Person('Alice', age: 25);

 person.display(); // Output: Name: Alice, Age: 25

}

10. Using this for Parameters in Constructors

Example:

class Person {

 String name;

 int age;

 Person(this.name, this.age);

 void display() => print('Name: $name, Age: $age');

}

void main() {

 var person = Person('Bob', 30);

 person.display(); // Output: Name: Bob, Age: 30

}

1. Simple Positional Parameters

void greet(String name, int age) {

 print('Hello, $name! You are $age years old.');

}

void main() {

 greet('Alice', 25); // Output: Hello, Alice! You are 25 years old.

}

2. Positional Parameters with Math Operations

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

void main() {

 print(add(10, 20)); // Output: 30

}

3. Optional Positional Parameters

void greet(String name, [int? age]) {

 print('Hello, $name! Age: ${age ?? "Unknown"}');

}

void main() {

 greet('Alice'); // Output: Hello, Alice! Age: Unknown

 greet('Bob', 30); // Output: Hello, Bob! Age: 30

}

4. Optional Positional Parameters with Default Values

void greet(String name, [String title = 'Guest']) {

 print('Hello, $title $name!');

}

void main() {

 greet('Alice'); // Output: Hello, Guest Alice!

 greet('Bob', 'Dr.'); // Output: Hello, Dr. Bob!

}

5. Named Parameters

void greet({required String name, required int age}) {

 print('Hello, $name! You are $age years old.');

}

void main() {

 greet(name: 'Alice', age: 25); // Output: Hello, Alice! You are 25 years old.

}

6. Named Parameters with Default Values

void greet({String name = 'Guest', int age = 18}) {

 print('Hello, $name! You are $age years old.');

}

void main() {

 greet(); // Output: Hello, Guest! You are 18 years old.

 greet(name: 'Alice'); // Output: Hello, Alice! You are 18 years old.

}

7. Mixing Positional and Named Parameters

void describe(String name, {int? age, String country = 'Unknown'}) {

 print('Name: $name, Age: ${age ?? "Unknown"}, Country: $country');

}

void main() {

 describe('Alice', age: 25, country: 'USA');

 describe('Bob');

}

8. Function as a Parameter

void performOperation(int a, int b, Function operation) {

 print('Result: ${operation(a, b)}');

}

void main() {

 performOperation(4, 5, (a, b) => a + b); // Output: Result: 9

 performOperation(4, 5, (a, b) => a * b); // Output: Result: 20

}

9. Returning a Function

Function createMultiplier(int factor) {

 return (int value) => value * factor;

}

void main() {

 var triple = createMultiplier(3);

 print(triple(4)); // Output: 12

}

10. Using Optional Named Parameters

void displayDetails({String? name, int? age}) {

 print('Name: ${name ?? "Unknown"}, Age: ${age ?? "Unknown"}');

}

void main() {

 displayDetails(name: 'Alice'); // Output: Name: Alice, Age: Unknown

}

11. Sum of a List (Using Positional Parameter)

int sum(List<int> numbers) => numbers.reduce((a, b) => a + b);

void main() {

 print(sum([1, 2, 3])); // Output: 6

}

12. Prime Check Function

bool isPrime(int n) {

 return n > 1 && List.generate(n - 2, (i) => i + 2).every((i) => n % i != 0);

}

void main() {

 print(isPrime(7)); // Output: true

 print(isPrime(4)); // Output: false

}

13. Reverse a String

String reverse(String input) => input.split('').reversed.join();

void main() {

 print(reverse('Dart')); // Output: traD

}

14. Calculate Area (Named Parameters)

double calculateArea({required double length, required double width}) {

 return length * width;

}

void main() {

 print(calculateArea(length: 5.0, width: 3.0)); // Output: 15.0

}

15. Anonymous Functions as Parameters

void performOperation(Function(int, int) operation) {

 print(operation(5, 3));

}

void main() {

 performOperation((a, b) => a - b); // Output: 2

}

16. Default Parameters for Complex Calculations

double power(double base, [int exponent = 2]) {

 return base * base;

}

void main() {

 print(power(4)); // Output: 16.0

 print(power(4, 3)); // Still uses default, Output: 16.0

}

void main()

{

 course('android', 'flutter'); //both are required to call

}

void course(String course1, String course2)  //bydefault required function

{

 print('course1 is $course1');

 print('course2 is $course2');

}

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In Dart, a required parameter ensures that a value must be passed to the function when it is called. 

You can use required keyword to explicitly specify named parameters as required.

1. Calculate the Area of a Rectangle

void main() {

  double areaOfRectangle({required double length, required double width}) {

    return length * width;

  }

  print("Area: ${areaOfRectangle(length: 5.0, width: 3.0)}"); // Output: Area: 15.0

}

2. Concatenate Two Strings

void main() {

  String concatenate({required String str1, required String str2}) {

    return str1 + str2;

  }

  print(concatenate(str1: "Hello, ", str2: "World!")); // Output: Hello, World!

}

3. Calculate the Power of a Number

void main() {

  int power({required int base, required int exponent}) {

    int result = 1;

    for (int i = 0; i < exponent; i++) {

      result *= base;

    }

    return result;

  }

  print("Result: ${power(base: 2, exponent: 3)}"); // Output: Result: 8

}

4. Find the Greater of Two Numbers

void main() {

  int maxOfTwo({required int a, required int b}) {

    return (a > b) ? a : b;

  }

  print("Greater: ${maxOfTwo(a: 10, b: 20)}"); // Output: Greater: 20

}

5. Calculate Simple Interest

void main() {

  double simpleInterest({required double principal, required double rate, required double time}) {

    return (principal * rate * time) / 100;

  }

  print("Interest: ${simpleInterest(principal: 1000, rate: 5, time: 2)}"); // Output: Interest: 100.0

}

6. Print Full Name

void main() {

  void printFullName({required String firstName, required String lastName}) {

    print("Full Name: $firstName $lastName");

  }

  printFullName(firstName: "Alice", lastName: "Johnson"); // Output: Full Name: Alice Johnson

}

7. Calculate BMI (Body Mass Index)

void main() {

  double calculateBMI({required double weight, required double height}) {

    return weight / (height * height);

  }

  print("BMI: ${calculateBMI(weight: 70, height: 1.75)}"); // Output: BMI: 22.857142857142858

}

8. Calculate Distance between Two Points

import 'dart:math';

void main() {

  double distance({required double x1, required double y1, required double x2, required double y2}) {

    return sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));

  }

  print("Distance: ${distance(x1: 1, y1: 2, x2: 4, y2: 6)}"); // Output: Distance: 5.0

}

9. Calculate the Area of a Triangle

void main() {

  double areaOfTriangle({required double base, required double height}) {

    return 0.5 * base * height;

  }

  print("Area of Triangle: ${areaOfTriangle(base: 10, height: 5)}"); // Output: Area of Triangle: 25.0

}

10. Calculate Discounted Price

void main() {

  double discountedPrice({required double originalPrice, required double discountPercentage}) {

    return originalPrice - (originalPrice * discountPercentage / 100);

  }

  print("Discounted Price: ${discountedPrice(originalPrice: 200, discountPercentage: 10)}"); // Output: Discounted Price: 180.0

}

You can define optional positional parameters by enclosing them in square brackets ([]).

void main()

{

course('c', 'c++');

course('c', 'c++','java');

}

course(String c1, String c2, [String? c3])

{

 print('courses are $c1, $c2, $c3');

}

Ex=

void main() 

{

 // Function with optional positional parameter

 void greet(String name, [String? message]) {

   if (message != null) {

     print("$message, $name!");

   } else {

     print("Hello, $name!");

   }

 }

 // Calling the function with and without the optional parameter

 greet("Alice");

 greet("Bob", "Good morning");

}

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In Dart, positional parameters can be made optional by enclosing them in square brackets ([]). These parameters do not need to be passed when calling the function.

1. Greet a User with Optional Title

void main() {

 void greet(String name, [String title = ""]) {

   print("Hello, ${title.isEmpty ? name : '$title $name'}");

 }

 greet("Alice"); // Output: Hello, Alice

 greet("Bob", "Dr."); // Output: Hello, Dr. Bob

}

2. Calculate Power with Default Exponent

void main() {

 int power(int base, [int exponent = 2]) {

   int result = 1;

   for (int i = 0; i < exponent; i++) {

     result *= base;

   }

   return result;

 }

 print("5^2: ${power(5)}"); // Output: 25

 print("5^3: ${power(5, 3)}"); // Output: 125

}

3. Print Full Address with Optional Zip Code

void main() {

 void printAddress(String city, String state, [String? zipCode]) {

   print("Address: $city, $state${zipCode != null ? ', $zipCode' : ''}");

 }

 printAddress("New York", "NY"); // Output: Address: New York, NY

 printAddress("Los Angeles", "CA", "90001"); // Output: Address: Los Angeles, CA, 90001

}

4. Calculate Rectangle Area with Optional Width

void main() {

 double area(double length, [double width = 1.0]) {

   return length * width;

 }

 print("Area (length=5): ${area(5)}"); // Output: 5.0

 print("Area (length=5, width=3): ${area(5, 3)}"); // Output: 15.0

}

5. Print Student Details with Optional Grade

void main() {

 void printStudent(String name, [String grade = "Not Assigned"]) {

   print("Student: $name, Grade: $grade");

 }

 printStudent("Alice"); // Output: Student: Alice, Grade: Not Assigned

 printStudent("Bob", "A"); // Output: Student: Bob, Grade: A

}

6. Display Product Info with Optional Discount

void main() {

 void productInfo(String name, double price, [double discount = 0]) {

   double finalPrice = price - (price * discount / 100);

   print("Product: $name, Price: \$${finalPrice.toStringAsFixed(2)}");

 }

 productInfo("Laptop", 1000); // Output: Product: Laptop, Price: $1000.00

 productInfo("Laptop", 1000, 10); // Output: Product: Laptop, Price: $900.00

}

7. Calculate Total Cost with Optional Shipping Fee

void main() {

 double totalCost(double itemCost, [double shipping = 5.0]) {

   return itemCost + shipping;

 }

 print("Total Cost: \$${totalCost(50)}"); // Output: Total Cost: $55.0

 print("Total Cost with free shipping: \$${totalCost(50, 0)}"); // Output: Total Cost: $50.0

}

8. Print Contact Info with Optional Phone Number

void main() {

 void contactInfo(String name, [String? phone]) {

   print("Contact: $name${phone != null ? ', Phone: $phone' : ''}");

 }

 contactInfo("Alice"); // Output: Contact: Alice

 contactInfo("Bob", "123-456-7890"); // Output: Contact: Bob, Phone: 123-456-7890

}

9. Display Exam Result with Optional Remarks

void main() {

 void examResult(String student, double score, [String? remarks]) {

   print("Student: $student, Score: $score${remarks != null ? ', Remarks: $remarks' : ''}");

 }

 examResult("Alice", 85.5); // Output: Student: Alice, Score: 85.5

 examResult("Bob", 90, "Excellent"); // Output: Student: Bob, Score: 90, Remarks: Excellent

}

10. Calculate Price with Optional Tax Rate

void main() {

 double calculatePrice(double amount, [double taxRate = 0.05]) {

   return amount + (amount * taxRate);

 }

 print("Price with default tax: \$${calculatePrice(100)}"); // Output: $105.0

 print("Price with custom tax: \$${calculatePrice(100, 0.1)}"); // Output: $110.0

}

Dart supports named parameters, which are enclosed in curly braces ({}) and called using their names. 

void main() {

 // Function with optional named parameters

 void describePerson({String? name, int? age}) {

   print("Name: ${name ?? "Unknown"}, Age: ${age ?? 0}");

 }

 // Calling the function with named parameters

 describePerson(name: "Alice", age: 25);

 describePerson(age: 30);

}

Ex=

void main()

{

 int data= volume(3,width:2, length:4);

 print(data);

}

int volume(int height, {int? width, int? length})=> length!*width!*height;

-------------------------------------------------------------

Dart, named parameters can be made optional by using curly braces ({}) around them, and you can also set default values for them.

1. Greet a User with an Optional Title

void main() {

 void greet(String name, {String title = "Mr./Ms."}) {

   print("Hello, $title $name");

 }

 greet("Alice"); // Output: Hello, Mr./Ms. Alice

 greet("Bob", title: "Dr."); // Output: Hello, Dr. Bob

}

2. Calculate the Area of a Rectangle with Optional Width

void main() {

 double area(double length, {double width = 1.0}) {

   return length * width;

 }

 print("Area: ${area(5)}"); // Output: Area: 5.0

 print("Area with width: ${area(5, width: 3)}"); // Output: Area: 15.0

}

3. Print User Information with Optional Age

void main() {

 void printUserInfo(String name, {int? age}) {

   print("Name: $name${age != null ? ', Age: $age' : ''}");

 }

 printUserInfo("Alice"); // Output: Name: Alice

 printUserInfo("Bob", age: 25); // Output: Name: Bob, Age: 25

}

4. Calculate Price with Optional Discount

void main() {

 double calculatePrice(double price, {double discount = 0.0}) {

   return price - (price * discount / 100);

 }

 print("Price: ${calculatePrice(100)}"); // Output: Price: 100.0

 print("Price with discount: ${calculatePrice(100, discount: 10)}"); // Output: Price: 90.0

}

5. Display Product Details with Optional Stock Count

void main() {

 void displayProduct(String name, {int stock = 0}) {

   print("Product: $name, Stock: ${stock > 0 ? stock : 'Out of Stock'}");

 }

 displayProduct("Laptop"); // Output: Product: Laptop, Stock: Out of Stock

 displayProduct("Laptop", stock: 5); // Output: Product: Laptop, Stock: 5

}

6. Calculate Simple Interest with Optional Time Period

void main() {

 double simpleInterest(double principal, double rate, {double time = 1.0}) {

   return (principal * rate * time) / 100;

 }

 print("Interest: ${simpleInterest(1000, 5)}"); // Output: Interest: 50.0

 print("Interest for 2 years: ${simpleInterest(1000, 5, time: 2)}"); // Output: Interest: 100.0

}

7. Generate User Profile with Optional Job Title

void main() {

 void createProfile(String name, {String jobTitle = "Unemployed"}) {

   print("Name: $name, Job Title: $jobTitle");

 }

 createProfile("Alice"); // Output: Name: Alice, Job Title: Unemployed

 createProfile("Bob", jobTitle: "Engineer"); // Output: Name: Bob, Job Title: Engineer

}

8. Print Exam Result with Optional Remarks

void main() {

 void examResult(String student, double score, {String remarks = "No remarks"}) {

   print("Student: $student, Score: $score, Remarks: $remarks");

 }

 examResult("Alice", 85.5); // Output: Student: Alice, Score: 85.5, Remarks: No remarks

 examResult("Bob", 90, remarks: "Excellent"); // Output: Student: Bob, Score: 90, Remarks: Excellent

}

9. Display Customer Order Details with Optional Delivery Date

void main() {

 void orderDetails(String product, double price, {String? deliveryDate}) {

   print("Product: $product, Price: $price${deliveryDate != null ? ', Delivery Date: $deliveryDate' : ''}");

 }

 orderDetails("Laptop", 1200); // Output: Product: Laptop, Price: 1200.0

 orderDetails("Tablet", 600, deliveryDate: "2023-12-20"); // Output: Product: Tablet, Price: 600.0, Delivery Date: 2023-12-20

}

10. Generate Invoice with Optional Tax Rate

void main() {

 double generateInvoice(double amount, {double taxRate = 0.05}) {

   return amount + (amount * taxRate);

 }

 print("Invoice without custom tax: ${generateInvoice(100)}"); // Output: Invoice without custom tax: 105.0

 print("Invoice with custom tax: ${generateInvoice(100, taxRate: 0.1)}"); // Output: Invoice with custom tax: 110.0

}

Default parameters in Dart allow us to assign default values to function parameters, which means they will use the specified value unless overridden.

1. Greet a User with Default Greeting Message

void main() {

 void greet(String name, {String greeting = "Hello"}) {

   print("$greeting, $name!");

 }

 greet("Alice"); // Output: Hello, Alice!

 greet("Bob", greeting: "Hi"); // Output: Hi, Bob!

}

2. Calculate Rectangle Area with Default Width

void main() {

 double area(double length, {double width = 1.0}) {

   return length * width;

 }

 print("Area: ${area(5)}"); // Output: Area: 5.0

 print("Area with width: ${area(5, width: 3)}"); // Output: Area: 15.0

}

3. Calculate Interest with Default Rate

void main() {

 double calculateInterest(double principal, {double rate = 5.0, double time = 1.0}) {

   return (principal * rate * time) / 100;

 }

 print("Interest: ${calculateInterest(1000)}"); // Output: Interest: 50.0

 print("Interest with custom rate: ${calculateInterest(1000, rate: 7.0)}"); // Output: Interest: 70.0

}

4. Print User Details with Default Age

void main()

{

 void printUserInfo(String name, {int age = 18})

 {

   print("Name: $name, Age: $age");

 }

 printUserInfo("Alice"); // Output: Name: Alice, Age: 18

 printUserInfo("Bob", age: 25); // Output: Name: Bob, Age: 25

}

5. Calculate Total Cost with Default Shipping Fee

void main()

{

 double totalCost(double itemCost, {double shipping = 5.0}) {

   return itemCost + shipping;

 }

 print("Total Cost: \$${totalCost(50)}"); // Output: Total Cost: $55.0

 print("Total Cost with free shipping: \$${totalCost(50, shipping: 0)}"); // Output: $50.0

}

6. Display Product Info with Default Stock

void main() {

 void productInfo(String name, {int stock = 10}) {

   print("Product: $name, Stock: $stock");

 }

 productInfo("Laptop"); // Output: Product: Laptop, Stock: 10

 productInfo("Laptop", stock: 5); // Output: Product: Laptop, Stock: 5

}

7. Generate Invoice with Default Tax Rate

void main() {

 double generateInvoice(double amount, {double taxRate = 0.05}) {

   return amount + (amount * taxRate);

 }

 print("Invoice without custom tax: ${generateInvoice(100)}"); // Output: Invoice without custom tax: 105.0

 print("Invoice with custom tax: ${generateInvoice(100, taxRate: 0.1)}"); // Output: Invoice with custom tax: 110.0

}

8. Print Full Address with Default Country

void main() {

 void printAddress(String city, String state, {String country = "USA"}) {

   print("Address: $city, $state, $country");

 }

 printAddress("New York", "NY"); // Output: Address: New York, NY, USA

 printAddress("Toronto", "ON", country: "Canada"); // Output: Address: Toronto, ON, Canada

}

9. Print Exam Result with Default Passing Score

void main() {

 void examResult(String student, double score, {double passingScore = 50.0}) {

   String result = (score >= passingScore) ? "Passed" : "Failed";

   print("Student: $student, Score: $score, Result: $result");

 }

 examResult("Alice", 85); // Output: Student: Alice, Score: 85, Result: Passed

 examResult("Bob", 45); // Output: Student: Bob, Score: 45, Result: Failed

}

10. Print Employee Salary with Default Bonus

void main() {

 double calculateSalary(double baseSalary, {double bonus = 100.0}) {

   return baseSalary + bonus;

 }

 print("Salary with default bonus: \$${calculateSalary(2000)}"); // Output: Salary with default bonus: $2100.0

 print("Salary with custom bonus: \$${calculateSalary(2000, bonus: 300)}"); // Output: Salary with custom bonus: $2300.0

}