Working With Text

This section deals with strings:

• Useful string methods

• Converting strings to numbers

• Converting numbers to strings

• The StringBuilder class

Useful String Methods

Formatting

• ToLower converts to lowercase

• ToUpper converts to uppercase

• Trim removes whitespace around the string

Searching

• IndexOf(x) returns index of first matching character or substring

• LastIndexOf returns index of last matching character or substring

Manipulating

• Substring(index, length) gets a substring

• Replace(input, output) replaces characters/substrings

Null checking

• String.IsNullOrEmpty(str)

• String.IsNullOrWhiteSpace(str)

Splitting

• str.Split(splitPoint)

Conversion

Converting strings to numbers

Very often when a user inputs something, it will be in a string format. You might want to convert that string to a number, especially if the input is meant to be a number.

string s = "1234";
int i = int.Parse(s); // method 1
int j = Convert.ToInt32(s); // method 2

Pro tip: If the string is null or just whitespace, int.Parse will throw an exception. In contrast, Convert.ToInt32 will return 0. For this reason, Convert.ToInt32 is often safer to work with.

Converting numbers to strings

Every integer has a ToString method that accepts an optional format string.

int i = 1234;
string s = i.ToString(); // "1234"
string t = i.ToString("C"); // "$1,234.00"
string u = i.ToString("C0"); // "$,234"

StringBuilder

In the System.Text namespace, there is a StringBuilder that allows you to create mutable strings.

In other words, it comes with a bunch of useful manipulation methods like Append or Insert or Remove. You use these on your builder instance, and it's like writing onto a piece of paper.

In contrast, while regular strings have these manipulation methods, they are more costly because they return a brand new string. So, if you're performing a lot of manipulations, it could be a good idea to use StringBuilder.

Note: Efficient string manipulation comes at the cost of having no searching methods. There are no methods like IndexOf or Contains or StartsWith.

using System.Text;

var builder = new StringBuilder();
builder.Append('-', 10);
builder.AppendLine();
builder.Append("Header");

// You can also chain methods!
builder
  .AppendLine();
  .Append('-', 10);
  .replace('-', '+');

// Prints
// ++++++++++
// Header
// ++++++++++
Console.WriteLine(builder);

// Although you don't have searching methods,
// StringBuilder still comes with index access
Console.WriteLine(builder[0]);