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Dart Functions

A function is a named block of code that does one job. A program calls the name to run that job.

Repeated lines without a function

Two greetings sit as two separate print lines in main. A new name means a new line written by hand.

void main() {
  print('Hello Ana');
  print('Hello Bo');
}

One function called twice

greet holds one print line and main calls it twice. Each call runs the body again.

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

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

A function with one parameter

The definition names one String parameter called name. Each call passes a different name into the same body.

void greet(String name) {
  print('Hello $name');
}

void main() {
  greet('Ana');
  greet('Bo');
}

A function with two parameters

add takes two int parameters and prints their sum. The two calls pass different pairs and get different sums.

void add(int a, int b) {
  print(a + b);
}

void main() {
  add(2, 3);
  add(10, 5);
}

Example

void showTotal(int price, int count) {
  print(price * count);
}

void main() {
  showTotal(3, 4);
  showTotal(2, 5);
}

Key points

  • A function is a named block of code that does one job.
  • A function definition sits above main in this course.
  • Parameters are the named inputs inside the round brackets of a definition.
  • Each parameter names a kind for the value it takes.
  • A call writes the function name and one value for each parameter.
  • void before a name marks a function that sends no value back.

In this example, showTotal takes a price and a count as its parameters. Its body prints the price times the count. The first call passes 3 and 4, so the print shows 12. The second call passes 2 and 5, so the print shows 10.

Note

main is a function too, and the program starts there.

Try it Yourself

Edit the code, then press Run.

Running is simulated · DartPad

Exercise

What does void before a function name mark?