Basic Functions

1. Definition:



Function is a logically grouped set of statements that perform a specific task. In Dart program, a function is created to achieve something. Every Dart program has at least one function i.e. main() where the execution of the program starts. It is a mandatory function in Dart.



2. Advantages of function:

• Avoid repetition of codes.

• Increases program readability.

• Divide a complex problem into simpler ones.

• Reduces chances of error.

• Modifying a program becomes easier by using function.



3. Syntax:


return_type function_name( parameters_list ){
    statement(s)
    return value;
}




• function_name : A function name to uniquely identify the function. Function naming follows the same rules of writing identifiers in Dart.
  

• parameters_list : Parameters (arguments) through which we pass values to a function. They are optional.
  

• return type : Type of Return value.
  A function with void as return type don't return any value.
  



4. Function call:



A function call can be made by using a call statement. A function call statement consists of function name and required argument enclosed in round brackets.

function_name ( parameters_list );



5. Types of functions:



1. Library functions :
   Library functions are the built in function that are already defined in the Dart library. For Example : print().

2. User-defined functions:
  Those functions that are defined by user to use them when required are called user-defined function.




6. Examples


1. Example 1 : Average Calculator



double average(List numbers) {

  double total = 0;

  for (int i = 0; i < numbers.length; i++) total += numbers[i];

  return total / numbers.length;

}

 

void main() {

  var list1 = [12, 15, 18, 19, 7];

  double average_list1 = average(list1);

  print(average_list1);

  var list2 = [3.14, 5.34, 12.0, 19.4];

  print(average(list2));

}





14.2
9.969999999999999



2. Example 2 : Random numbers generator (Without Parameters)



import 'dart:math';

 

List randomGenerator() {

  var randoms = [];

  for (int i = 0; i < 5; i++) {

    int x = Random().nextInt(100);

    randoms.add(x);

  }

  return randoms;

}

 

void main() {

  print(randomGenerator());

  var l1 = randomGenerator();

  print(l1);

}





[70, 21, 24, 7, 94]
[23, 57, 55, 42, 22]



3. Example 3 : Print a message (Void Function)



void show(object, quantity) {

  print("You have $quantity $object in storage");

}

 

void main() {

  show("Pictures", 23);

  show("Documents", 11);

  show("Videos", 5);

}





You have 23 Pictures in storage
You have 11 Documents in storage
You have 5 Videos in storage



4. Example 4 : helloWorld (void function without Parameters)



void helloWorld() {

  print("Hello Flutter Pro students <3");

}

 

void main() {

  helloWorld();

}





Hello Flutter Pro students <3




Note:

For functions that contain just one expression, you can use a shorthand syntax:




void helloWorld() => print("Hello World");