C# Strings

A string is a sequential collection of characters that is used to represent text.

Declaring a variable to contain a string

Strings are surrounded by double quotes: "

var name = "Suncoast Developers Guild";
var description = "Code School in St Petersburg, FL";

Appending strings

We can append two strings using the + operator.

var name = "Suncoast Developers Guild";
var description = "Code School in St Petersburg, FL";
var message = name + " is a " + description;

Interpolating strings

We can incorporate variables and expressions into a string by making an interpolated string.

Note: Interpolated strings start with a $

var name = "Suncoast Developers Guild";
var description = "Code School in St Petersburg, FL";
var message = $"{name} is a {description}";
var mathProblem = $"What do you get when you multiply six by 9: {6 * 9}"

String length

We can get the length of a string by using the length property.

var name = "Suncoast Developers Guild";
var nameLength = name.Length;
Console.WriteLine(nameLength);
// Output: 25

Iterating the characters in a string

We can iterate over a string and assess each character with a foreach loop.

var name = "Mary";
foreach (var character in name)
{
  Console.WriteLine(character);
}
// Output:
// M
// a
// r
// y

Using a for loop

Alternatively, we can use the string length to use a for loop and access each character by its index.

var name = "Mary";
for (var index = 0; index < name.Length; index++)
{
  Console.WriteLine(name[index]);
}
// Output:
// M
// a
// r
// y

Using LINQ

If you add using System.Linq to your code you may use LINQ to iterate through a string. All of the methods for LINQ are available to you and it treats the string as a sequence of characters. In this example we use the ability for LINQ to Select (transform) a sequence (in this case characters) into a new list. We also use the ability to have the index provided as well.

var name = "Mary";
var newList = name.Select((character, index) => $"The character at index {index} is {character}");
// The value of newList is:
// [
//   "The character at index 0 is M",
//   "The character at index 1 is a",
//   "The character at index 2 is r",
//   "The character at index 3 is y"
// ]

Splitting a string

We can split a string into an array of strings using the Split method. The first parameter will be the character you want to split the string on.

var sentence = "Today is a beautiful day";
var words = sentence.Split(' ');
// The effect would be:
// words = ['Today', 'is', 'a', 'beautiful', 'day'];

Replacing text in a string

We can replace parts of strings with new values by using the replace method.

var sentence = "Today is a beautiful day";
sentence.Replace("beautiful", "sunny");
// The effect would be:
// sentence = "Today is a sunny day";

Reversing a string

We can reverse the order of characters in a string by using the reverse method.

var name = "Suncoast Developers Guild".
var reverseName = name.Reverse();
// The effect would be:
// reverseName = "dliuG srepoleveD tsaocnuS";

Changing the case of a string

We can make all characters in a string upper case or lowercase with the ToUpper and ToLower methods.

var name = "Suncoast Developers Guild";
var upperName = name.ToUpper();
var lowerName = name.ToLower();
// The effects would be:
// upperName = "SUNCOAST DEVELOPERS GUILD";
// lowerName = "suncoast developers guild";

Getting a sub-string

We can get part of a string by using the substring method.

NOTE: The first number in the method is the starting index, the second number is how many characters to return.

var movie = "The Avengers: Endgame";
var subtitle = movie.Substring(14, 7);
// The effect would be:
// subtitle = "Endgame";

Does a string contain another string

We can check to see if one string is contained in another string by using the contains method.

var movieDescription = "Thanos attempts to gather all infinity stones to end the Avengers for good.";
var containsInfinity = movieDescription.Contains("infinity");
var containsHulk = movieDescription.Contains("Hulk");
// The effects would be:
// containsInfinity = true;
// containsHulk = false;

EndsWith

We can check if a string ends with a certain substring by using the EndsWith method.

var headline = "Fundraising night was a huge success!";
var endsWithExclamation = headline.EndsWith("!");
// The effect would be:
// endsWithExclamation = true;

StartsWith

We can also check if a string starts with a certain substring by using StartsWith method.

var greeting = "Welcome to our home!"
var startsWithHello = greeting.StartsWith("Hello");
// The effect would be:
// startsWithHello = false;

Join

We can join an array of strings back into a single string using the String.Join method.

var studentNames = new string[5] {"Marcus", "Emily", "Jason", "Steve", "Julia"};
var studentString = String.Join(", ", studentNames);
// The effect would be:
// studentString = "Marcus, Emily, Jason, Steve, Julia";

Pad + Trim

You can add and remove characters to the beginning and end of strings with PadLeft, PadRight and Trim methods.

NOTE: Trim will automatically trim the left and right sides of a string.

var museumName = "Salvador Dali Museum";
var paddedName = museumName.PadLeft(3, '*');
// The effect would be:
// paddedName = "***Salvador Dali Museum";
paddedName = paddedName.PadRight(3, '*');
// The effect would be:
// paddedName = "***Salvador Dali Museum***";
var trimmedName = paddedName.Trim('*');
// The effect would be:
// trimmedName = "Salvador Dali Museum";