C# Arrays and Lists

Arrays and lists let you keep many values of the same type together under one name.

Arrays

An array has a fixed size. Create it with values in curly braces:

Example

csharp

string[] students = { "Ali", "Ayesha", "Bilal" };
int[] marks = { 81, 94, 67 };

Console.WriteLine(students[0]);
Console.WriteLine(marks[2]);

marks[2] = 72;
Console.WriteLine(marks[2]);
Console.WriteLine($"Count: {marks.Length}");

Output

Ali
67
72
Count: 3

You can also create an empty array of a set size. Every number starts at 0:

Example

csharp

int[] scores = new int[5];

Using an index outside the array, like marks[3] in an array of 3 items, throws an IndexOutOfRangeException. Valid indexes are 0 to Length - 1.

Looping and Sorting Arrays

Example

csharp

int[] prices = { 750, 120, 990, 300 };
Array.Sort(prices);

foreach (int p in prices)
{
    Console.Write(p + " ");
}
Console.WriteLine();
Console.WriteLine($"Cheapest: {prices[0]}");

Output

120 300 750 990 
Cheapest: 120

Lists

A List<T> is like an array that can grow and shrink. The T is the type of items, for example List<string>:

Example

csharp

List<string> cart = new List<string> { "Sugar", "Tea" };

cart.Add("Milk");
cart.Add("Biscuits");
cart.Remove("Tea");

Console.WriteLine($"Items: {cart.Count}");
foreach (string item in cart)
{
    Console.WriteLine("- " + item);
}
Console.WriteLine(cart.Contains("Milk"));

Output

Items: 3
- Sugar
- Milk
- Biscuits
True

List lives in the System.Collections.Generic namespace. New console projects include it automatically; in older projects add using System.Collections.Generic; at the top.

Common List Methods

Member	What it does
`list.Add(x)`	Adds an item at the end
`list.Insert(i, x)`	Adds an item at position i
`list.Remove(x)`	Removes the first matching item
`list.RemoveAt(i)`	Removes the item at position i
`list.Count`	Number of items
`list.Contains(x)`	True if the item is in the list
`list.Sort()`	Sorts the list
`list.Clear()`	Removes everything

Array or List?

	Array	List
Size	Fixed	Grows and shrinks
Number of items	`Length`	`Count`
Best for	Data that never changes size	Most everyday code

Quick Calculations

The System.Linq methods give quick answers about arrays and lists:

Example

csharp

List<int> results = new List<int> { 55, 78, 91, 64 };

Console.WriteLine(results.Max());
Console.WriteLine(results.Min());
Console.WriteLine(results.Sum());
Console.WriteLine(results.Average());

Output

Exercise

Which property gives the number of items in a List?

LengthSizeCountTotal