Reading User Input

In a command-line program, stdin.readLineSync() from dart:io waits for the user to type a line and press Enter. It returns a String? — null if there's no more input.

Example

import 'dart:io';

void main() {
  stdout.write("What's your name? ");
  final name = stdin.readLineSync() ?? '';
  print('Nice to meet you, $name!');
}

Expected output

What's your name? Ada
Nice to meet you, Ada!

(Ada is what the user typed.) stdout.write keeps the cursor on the same line as the question.

Reading numbers

import 'dart:io';

void main() {
  stdout.write('How old are you? ');
  final age = int.tryParse(stdin.readLineSync()?.trim() ?? '');

  if (age == null) {
    print('Please enter a whole number.');
    return;
  }

  print("In ten years you'll be ${age + 10}.");
}

Note: DartPad, Flutter apps, and web apps don't read keyboard input this way. Run these examples with dart run in a terminal.

Practice

Ask the user for their favorite color and print it back in capitals: BLUE is a great color!.

import 'dart:io';

void main() {
  stdout.write('Favorite color? ');
  final color = stdin.readLineSync() ?? '';
  print('${color.toUpperCase()} is a great color!');
}