List Exercises

Practice working with Lists in Dart through hands-on exercises

Exercise Overview

This exercise demonstrates how to work with Lists in Dart using functions. You’ll learn to:

• Create and populate lists with user input
• Pass lists to functions
• Iterate through lists and display their contents

Problem Statement

Create a program that:

1. Create an empty list

   Initialize an empty list of integers

2. Get user input

   Use a function to ask the user for 10 integer values and add them to the list

3. Display the list

   Use another function to print each element of the list

Solution Approach

Function 1: Getting User Input

This function receives a list, populates it with 10 user-provided integers, and returns the modified list:

import 'dart:io';

List<int> pedirNumeros(List<int> numeros){
  for (var i = 0; i < 10; i++) {
    print('Introducir un Valor Entero:');
    numeros.add(int.parse(stdin.readLineSync()!));
  }
  return numeros;
}

When you pass a list to a function in Dart, you’re passing a reference to the list. This means modifications inside the function affect the original list.

Function 2: Displaying the List

This function iterates through the list and prints each value:

void imprimirLista(List<int> numeros){
  for (var numero in numeros) {
    print('El Valor es: $numero');
  }
}

The for-in loop is perfect for iterating through all elements in a collection when you don’t need the index.

Main Function

The main function coordinates the program flow:

void main() {
  List<int> numeros = [];
  pedirNumeros(numeros);
  imprimirLista(numeros);
}

Complete Program

/* Hacer un programa que empleando funciones cree una lista de números enteros y la cargue con 10 valores enteros dados por el usuario.
Ya con la lista cargada imprima cada uno de los elementos de dicha lista.*/

import 'dart:io';

List<int> pedirNumeros(List<int> numeros){
  for (var i = 0; i < 10; i++) {
    print('Introducir un Valor Entero:');
    numeros.add(int.parse(stdin.readLineSync()!));
  }
  return numeros;
}

void imprimirLista(List<int> numeros){
  for (var numero in numeros) {
    print('El Valor es: $numero');
  }
}

void main() {
  List<int> numeros = [];
  pedirNumeros(numeros);
  imprimirLista(numeros);
}

Key Concepts

List Declaration

List<int> numeros = [] creates an empty list of integers

Adding Elements

Use .add() method to append elements to a list

For-In Loop

for (var item in list) iterates through each element

Type Safety

List<int> ensures only integers can be added to the list

List Operations Explained

Why return the list if it's already modified?

In Dart, lists are reference types. When you pass a list to a function and modify it, the changes affect the original list. Returning the list is optional but makes the function’s behavior more explicit and allows for method chaining.

// Both work the same way
pedirNumeros(numeros);
// or
numeros = pedirNumeros(numeros);

What's the difference between for and for-in?

Regular for loop:

for (var i = 0; i < numeros.length; i++) {
  print(numeros[i]);
}

Use when you need the index.

For-in loop:

for (var numero in numeros) {
  print(numero);
}

Use when you only need the values.

How to handle invalid input?

Add error handling to make the program more robust:

List<int> pedirNumeros(List<int> numeros){
  for (var i = 0; i < 10; i++) {
    print('Introducir un Valor Entero:');
    try {
      numeros.add(int.parse(stdin.readLineSync()!));
    } catch (e) {
      print('Error: Introduce un número válido');
      i--; // Retry this iteration
    }
  }
  return numeros;
}

Enhanced Version

Here’s an enhanced version with additional features:

import 'dart:io';

List<int> pedirNumeros(List<int> numeros, int cantidad){
  for (var i = 0; i < cantidad; i++) {
    print('Introducir valor ${i + 1} de $cantidad:');
    numeros.add(int.parse(stdin.readLineSync()!));
  }
  return numeros;
}

void imprimirLista(List<int> numeros){
  print('\n=== Lista de Números ===');
  for (var i = 0; i < numeros.length; i++) {
    print('Posición $i: ${numeros[i]}');
  }
  print('\nTotal de elementos: ${numeros.length}');
}

void main() {
  List<int> numeros = [];
  pedirNumeros(numeros, 10);
  imprimirLista(numeros);
}

Practice Challenges

Challenge 1

Modify the program to also calculate and display the sum and average of all numbers entered.

Challenge 2

Add a function to find and display the maximum and minimum values in the list.

Challenge 3

Create a function to sort the list in ascending order before printing.

Challenge 4

Add a function to remove duplicate values from the list.