c-sharp.md

C#

Data types

Primitives (int, char, float, byte, etc.) and custom structs are value types.

• Accessed by value
• Allocated on the stack
• Instantly removed when they go out of scope

Array, strings, and custom classes are reference types.

• Accessed by reference
• Allocated on the heap
• Marked for garbage collection when they go out of scope

var a = ["a", "b"];
var b = a;
a[0] = "c";
Console.WriteLine(b[0]); // "c"

To convert from one type to another:

var a = 1; // declare an integer
var b = (byte)a; // convert it to a byte

For more advanced conversions, use the Convert class, which does things like Convert.ToByte() and Convert.ToInt32.

Strings

Strings in C# are immutable.

Combining strings

var firstName = "James";
var lastName = "Harris";

var concatFullName = firstName + " " + lastName;
var interpolFullName = string.Format("{0} {1}", firstName, lastName);

var nameArray = new string[2] {firstName, lastName};
var joinedFullName = string.Join(" ", nameArray);

Verbatim strings

Escape characters such as \ do not apply within verbatim strings.

var standardStringPath = "System path: \n C:\\Windows\\System";
var verbatimStringPath = @"System path: 
C:\Windows\System";

String interpolation

var firstName = "James";
var lastName = "Harris";
var fullName = $"{firstName} {lastName}";

Arrays

Once declared, arrays in C# are of a fixed size and type. If you don't know how long the array should be, use a list.

var emptyArray = new int[3];
var prefilledArray = new[] { 1, 2, 3 };

To find an item in an array:

var index = Array.IndexOf(arr, 3); // 2

To check if an array contains an item:

using System.Linq;

prefilledArray.Contains(3); // true

Multidimensional arrays

Rectangular arrays

var matrix = new int[2, 5]
{
	{ 1, 2, 3, 4, 5 },
	{ 6, 7, 8, 9, 10 }
};

Jagged arrays

var matrix = new int[3][];
matrix[0] = new int[3] { 1, 2, 3 };
matrix[1] = new int[2] { 1, 2 };
matrix[2] = new int[4] { 1, 2, 3, 4 };

Lists

Lists are like variable-size arrays.

using System.Collections.Generic;

var emptyList = new List<int>();
var prefilledList = new List<int>() { 1, 2, 3 };

emptyList.Add(1);
emptyList.Add(someArray);

To find an item in a list:

var index = prefilledList.IndexOf(3); // 2

Instead of .Length, lists use .Count.

prefilledList.Count // 3

Methods for collections (lists and arrays)

To convert everything in a collection to a different type, use .Select():

var intList = strList.Select(x => Convert.ToInt32(x)).ToList();

To list all items in a collection:

foreach (var item in list) { Console.Write($"{item} "); }
Console.WriteLine();

Enums

Collections of constants. Defaults to the int type.

namespace StarWars
{
	public enum Episodes
	{
		ThePhantomMenace = 1,
		AttackOfTheClones = 2,
		RevengeOfTheSith = 3,
		ANewHope = 4,
		TheEmpireStrikesBack = 5,
		ReturnOfTheJedi = 6,
		TheForceAwakens = 7,
		TheLastJedi = 8
	}
	class Program
	{
		static void Main()
		{
			var bestEpisode = (Episodes)6; // ReturnOfTheJedi
		}
	}
}

File operations

using System.IO;

File provides static methods. These can be used without setting up a FileInfo object.

var path = @"C:\somefile.txt";
File.Exists(path);
File.Copy(path, path2);
var content = File.ReadAllText(path);

FileInfo provides instance methods. You instantiate it with a path and call methods on the instance. This provides a performance benefit if you need to provide multiple operations on one file.

var file = new FileInfo(path);
if (file.Exists) {
	file.copyTo(path2);
}

Useful methods:

• Create()
• Copy()
• Delete()
• Exists()
• GetAttributes()
• Move()
• ReadAllText()

Directory() and DirectoryInfo() follow similar principles. To list files in a folder:

var files = Directory.GetFiles(@"D:\Repositories\handbook", "*.html", SearchOption.AllDirectories);
foreach (var file in files) {
	Console.WriteLine(file);
}

We also have the Path() class, which provides tools for working with a string that represents a path.

Debugging

Logging several values with labels:

Console.WriteLine(string.Format("var1: {0}, var2: {1}", var1, var2));

Misc

Generating random numbers

var random = new Random();
var myRandomNumber = random.Next(); // outputs integer between 1 and INT_MAX
var randomBetween1and10 = random.Next(1, 10);