A Simple Interactive Program
Let’s study the command line to pass input to an application in Dart.
We'll cover the following...
Overview
In many cases, we come upon scenarios where we need to take input from the user and print that input onto the console
Let’s write a program for a personalized greeting application. The program will ask the user for their name and then display a personalized greeting for that user.
The coding program in this lesson requires input from the user in order for it to execute successfully.
After you have typed the input, press RUN to execute the program.
import 'dart:io';main() {print("Hello " + stdin.readLineSync());}
Understanding the Code
The code above might look a bit intimidating. But don’t worry; let’s go over it one line at a time.
Libraries
On line 1 of the code above, we are importing the dart:io library.
In computer programming, a library is a collection of similar code that you can reference in your own code. When you import a library, you can access all the code in that library.
Every library has a particular purpose. The dart:io library provides I/O (Input/Output) support for non-web applications. We imported dart:io because the program we wrote requires input from the user.
Taking Input in Dart
Dart provides multiple methods that can be used to take external input from a user depending on the type of input required by the program. For this course, we will be using the readLineSync() method (function) which reads a line from the input.
The complete expression we will use is stdin.readLineSync(). stdin stands for standard input, letting the compiler know that the program specifically requires some sort of input from the user. readLineSync() is a built-in method that we have already discussed above.
Line 4 is displaying Hello and then concatenating (joining) it with the input provided by the user using the addition (+) operator (a topic we will discuss later in the course).
That’s pretty much all there is to the code written above.