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Documentation Index

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Introduction

In Dart, you can read user input from the console using the stdin object from the dart:io library. This is essential for creating interactive command-line applications.

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Reading String Input

To read text input from the user, use stdin.readLineSync(): 
import 'dart:io';

void main() {
  print("¿Cómo te llamas?");
  
  // El '?' es porque el valor puede ser nulo
  String? nombre = stdin.readLineSync();

  print("Hola, $nombre. ¡Mucho gusto!");
}
The return type is String? (nullable) because readLineSync() can return null if the input stream is closed or if an error occurs.

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Reading Numeric Input

To read numeric values, you need to:
1

Read the input as a string

Use stdin.readLineSync() to get the user’s input
2

Parse the string to a number

Use int.parse() or double.parse() to convert the string to a number
3

Handle the nullable value

Use the ! operator to assert that the value is not null

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Reading Integers

import 'dart:io';

void main() {
  print("Introduce tu edad:");
  
  // Leemos el texto y lo convertimos a entero
  int edad = int.parse(stdin.readLineSync()!);

  print("El año que viene tendrás ${edad + 1} años.");
}

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Complete Example

Here’s a complete program that demonstrates reading both string and numeric input: 
import 'dart:io';

void main() {
  print("¿Cómo te llamas?");
  
  // El '?' es porque el valor puede ser nulo
  String? nombre = stdin.readLineSync();

  print("Hola, $nombre. ¡Mucho gusto!");

  //Introducir valores numericos int o double
  print("Introduce tu edad:");
  
  // Leemos el texto y lo convertimos a entero
  int edad = int.parse(stdin.readLineSync()!);

  print("El año que viene tendrás ${edad + 1} años.");
}

​
Key Points

Import Required

Always import dart:io to access stdin

Nullable by Default

readLineSync() returns String? which must be handled

Parse Numbers

Use int.parse() or double.parse() for numeric input

Null Assertion

Use ! operator when you’re sure the input won’t be null

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Best Practices

When using the ! operator, make sure the input won’t be null. Otherwise, your program will crash with a null reference error.
For more robust applications, consider using try-catch blocks when parsing numeric input to handle invalid input gracefully.
import 'dart:io';

void main() {
  print("Introduce tu edad:");
  
  try {
    int edad = int.parse(stdin.readLineSync()!);
    print("El año que viene tendrás ${edad + 1} años.");
  } catch (e) {
    print("Error: Por favor introduce un número válido");
  }
}

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