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Lists

Recap

  • In the first lesson we already covered collections quickly:
var names = new List<string> { "World", "Ana", "Felipe" };
foreach (var name in names)
{
  Console.WriteLine($"Hello {name.ToUpper()}!");
}
  • A List is a type of collection we can store add and remove values from

Adding and removing values

  • We can add values to a list with .Add() method, let's put that in practice:
var names = new List<string> { "World", "Ana", "Felipe" };
names.Add("Maria");
names.Add("Bill");
foreach (var name in names)
{
  Console.WriteLine($"Hello {name.ToUpper()}!");
}
  • When we want to remove items from the list we use .Remove()
var names = new List<string> { "World", "Ana", "Felipe", "Maria", "Bill" };
names.Remove("World");
foreach (var name in names)
{
  Console.WriteLine($"Hello {name.ToUpper()}!");
}

Index

  • Every item in the list has an index starting with 0, think of them as a way to specify items in a list:
var names = new List<string> { "Ana", "Felipe", "Maria", "Bill" };
Console.WriteLine($"Our first item changed to {names[0]}.");
Console.WriteLine($"I've added {names[2]} and {names[3]} to the list.");

  • As you can see we can use square brackets to call upon a value using its index, for this example [0,1,2,3]

  • Another useful method is .Count:

var names = new List<string> { "Ana", "Felipe", "Maria", "Bill" };
Console.WriteLine($"The list has {names.Count} people in it");
  • The Count method will return the amount of values that are in the List, 4 in this case

Searching lists

  • If we want to look for a certain value in a List we can use the .IndexOf() method:
var names = new List<string> { "Ana", "Felipe", "Maria", "Bill" };
var index = names.IndexOf("Felipe");
if (index != -1)
  Console.WriteLine($"The name {names[index]} is at index {index}");

var notFound = names.IndexOf("Not Found");
  Console.WriteLine($"When an item is not found, IndexOf returns {notFound}");

  • When using "IndexOf" the method will look for an exact match in the list and return it's index

  • If no match is found, the method will return the value "-1"

  • In the example above we use the returned value in an IF ELSE branch to console log if the search was succesful

Sorting Lists

  • When we have large lists it might be useful to sort them:
var names = new List<string> { "Ana", "Felipe", "Maria", "Bill" };
names.Sort();
foreach (var name in names)
{
  Console.WriteLine($"Hello {name.ToUpper()}!");
}
  • The .Sort() method will rearrange the values in the list to alphabetical order if they are strings

Exercise

  • The same way we can create Lists for strings, we can create lists of integers

  • For this case lets output all the Fibonacci Numbers in console

  • Fibonacci numbers start with [1, 1] and every number after it is the sum of the last 2 numbers, so: [1,1,2,3,5,8,...1836311903]

  • You will probably need a loop for this one

  • Just so you do not brick your console or potato I will provide you with the largest Fibonacci number C# can calculate from integers: 1836311903

Solution

  • You can check one of the many solutions HERE

  • You should have the following output in your console:

1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 28657 46368 75025 121393 196418 317811 514229 832040 1346269 2178309 3524578 5702887 9227465 14930352 24157817 39088169 63245986 102334155 165580141 267914296 433494437 701408733 1134903170 1836311903

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