Types of Functions in Dart

Types Of Function

Functions are the block of code that performs a specific task. Here are different types of functions:

• No Parameter And No Return Type
• Parameter And No Return Type
• No Parameter And Return Type
• Parameter And Return Type

Function With No Parameter And No Return Type

In this function, you do not pass any parameter and expect no return type. Here is an example of it:

Example 1: No Parameter & No Return Type

Here printName() is a function which prints name on screen.

void main() {
  printName();
}

void printName() {
  print("My name is John Doe.");
}

My name is John Doe.

In this program, printName() is the function which has keyword void. It means it has no return type, and the empty pair of parentheses implies that there is no parameter that is passed to the function.

Example 2: No Parameter & No Return Type

Here printPrimeMinisterName() is a function which prints prime minister name on screen.

void main() {
  print("Function With No Parameter and No Return Type");
  printPrimeMinisterName();
}

void printPrimeMinisterName() {
  print("John Doe.");
}

Function With No Parameter and No Return Type
John Doe.

Function With Parameter And No Return Type

In this function, you do pass the parameter and expect no return type. Here is an example of it:

Example 1: Parameter & No Return Type

Here printName(String name) is a function which welcome person.

void main() {
  printName("John");
}

void printName(String name) {
  print("Welcome, ${name}.");
}

Welcome, John.

In this program, printName(String name) is the function which has keyword void. It means it has no return type, and the pair of parentheses is not empty but this time that suggests it to accept an parameter.

Example 2: Parameter & No Return Type

Here add(int a, int b) is a function that finds and prints the sum of two numbers.

// This function add two numbers
void add(int a, int b) {
  int sum = a + b;
  print("The sum is $sum");
}

void main() {
  int num1 = 10;
  int num2 = 20;

  add(num1, num2);
}

The sum is 30

Function With No Parameter And Return Type

In this function, you do not pass any parameter but expect return type. Here is an example of it:

Example 1: No Parameter & Return Type

Here primeMinisterName() is a function which returns prime minister name. In the entire program, anyone can use this function to find the name of the prime minister.

void main() {
// Function With No Parameter & Return Type
void main() {
  String name = primeMinisterName();
  print("The Name from function is $name.");
}

String primeMinisterName() {
  return "John Doe";
}

The name from function is John Doe

In this program, primeMinisterName() is the function which has String keyword before function name, means it return String value, and the empty pair of parentheses suggests that there is no parameter that is passed to the function.

Example 2: No Parameter & Return Type

Here voterAge() is a function which returns minimum voter age.

// Function With No Parameter & Return Type
void main() {
  int personAge = 17;

  if (personAge >= voterAge()) {
    print("You can vote.");
  } else {
    print("Sorry, you can't vote.");
  }
}

int voterAge() {
  return 18;
}

Sorry, you can't vote.

Function With Parameter And Return Type

In this function, you do pass the parameter and also expect return type. Here is an example of it:

Example 1: Parameter & Return Type

Here add(int a, int b) is a function that returns its sum in integer. We can display results in our main function.

// this function add two numbers
int add(int a, int b) {
  int sum = a + b;
  return sum;
}

void main() {
  int num1 = 10;
  int num2 = 20;

  int total = add(num1, num2);
  print("The sum is $total.");
}

The sum is 30.

In this program, int add(int a, int b) is the function with int as the return type, and the pair of parenthesis has two parameters, i.e., a and b.

Example 2: Parameter & Return Type

Here calculateInterest(double principal, double rate, double time) is a function that returns its simple interest in double. We can display results in our main function.

// function that calculate interest
double calculateInterest(double principal, double rate, double time) {
  double interest = principal * rate * time / 100;
  return interest;
}

void main() {
  double principal = 5000;
  double time = 3;
  double rate = 3;
  double result = calculateInterest(principal, rate, time);
  print("The simple interest is $result.");
}

The simple interest is 450.0.

Complete Example

Here is the program, which includes all types of functions we studied earlier.

// parameter and return type
int add(int a, int b) {
  var total;
  total = a + b;
  return total;
}

// parameter and no return type
void mul(int a, int b) {
  var total;
  total = a * b;
  print("Multiplication is : $total");
}

// no parameter and return type
String greet() {
  String greet = "Welcome";
  return greet;
}

// no parameter and no return type
void greetings() {
  print("Hello World!!!");
}

void main() {
  var total = add(2, 3);
  print("Total sum: $total");
  mul(2, 3);
  var greeting = greet();
  print("Greeting: $greeting");
  greetings();
}

Total sum: 5
Multiplication is : 6
Greeting: Welcome
Hello World!!!

Video

Watch our video on functions types in Dart.