Defining functions

Learn how to define and call a function.

Defining functions

In Dart a function is declared as returnType name(params) { ... }. When there is no value to return, write void. Example: void greet() { print('Hello'); }.

You call a function by its name followed by parentheses: greet();. When this line runs, the function body executes. Parentheses are required even when the function takes no parameters.

Functions group code: you write a task once and call it from many places. This reduces repetition and improves readability. Parameters and return values are detailed in the next lessons.

Calling and parentheses

To call a function you write its name followed by parentheses. When it takes no parameters, the parentheses stay empty: greet();. Without parentheses, greet; alone is a reference to the function, not a call.

This distinction matters later with first-class functions; you will see the details soon. For now: to run it, add the parentheses.

A call works as long as the definition appears before it. Dart must have seen the function definition by the time it is called. Calling other functions from main is the standard layout of a Dart program.

Exercise Write and call greet

Define a greet function whose body calls print('Hello'). Add a greet() call inside main.

Show example solution

void greet() {
  print('Hello');
}

void main() {
  greet();
}

Test yourself

What is written when there is no return value?
```
void greet() { print('Hello'); }
```
- int
- var
- void
- null
Show answer

void — void marks that there is no return value.
Match the function parts

void

No return
greet

Function name
()

No parameters
greet();

Call

Function definition

void greet() {
  print(____);
}
void main() { greet(); }

Show answer

void greet() {
  print('Hello');
}
void main() { greet(); }

Next lesson: Return values

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