String Methods in C

The string class in C# provides a variety of methods and properties for handling and processing strings. Below are some commonly used methods along with examples and explanations.

Comparing Strings

Using Equals()

The Equals() method checks if two strings are equal. It works similarly to the == operator but is generally preferred when dealing with objects.

string word1 = "C#";
string word2 = "c#";

Console.WriteLine(word1.Equals("C#"));  // True
Console.WriteLine(word1.Equals(word2)); // False
Console.WriteLine(word1 == "C#");       // True
Console.WriteLine(word1 == word2);      // False

Note

String comparison using Equals() is case-sensitive. To perform a case-insensitive comparison, use Equals(word2, StringComparison.OrdinalIgnoreCase).

Using CompareTo()

The CompareTo() method compares two strings based on their lexicographical order (dictionary order).

• It returns -1 if the first string is less than the second.
• It returns 0 if they are equal.
• It returns 1 if the first string is greater than the second.

string word1 = "Aardvark";
string word2 = "Adam";

Console.WriteLine(word1.CompareTo(word2)); // -1

Tip

Remember that lowercase letters come after uppercase letters in ASCII order.

Concatenation

Joining strings together can be done using the + operator or the Concat() method.

string hello = "Hello";
string world = "World";

Console.WriteLine(hello + " " + world);             // "Hello World"
Console.WriteLine(string.Concat(hello, " ", world)); // "Hello World"

Concatenation with Other Data Types

string message = "Your age is ";
int age = 17;

message += age;  // "Your age is 17"
Console.WriteLine(message);

Note

Avoid excessive use of + for string concatenation in loops, as it can affect performance. Consider using StringBuilder for repeated modifications.

Changing Case

The methods ToUpper() and ToLower() convert all characters in a string to their uppercase or lowercase equivalents.

string password = "qwertyuiop";
Console.WriteLine(password.ToUpper());  // "QWERTYUIOP"

Use these methods for case-insensitive string comparisons or standardizing input.

Searching for a Substring

Using IndexOf()

The IndexOf() method searches for the first occurrence of a substring within a string and returns its index. It returns -1 if the substring is not found.

string title = "Introduction to Computer Science";
Console.WriteLine(title.IndexOf("tro"));  // 2
Console.WriteLine(title.IndexOf("COMPUTER"));  // -1 (case-sensitive)

Tip

Searches are case-sensitive. Convert both strings to the same case using ToUpper() or ToLower() for a case-insensitive search.

Using LastIndexOf()

LastIndexOf() returns the index of the last occurrence of a substring within the string.

string text = "This is a test. This is only a test.";
Console.WriteLine(text.LastIndexOf("test"));  // 27

Extracting a Substring

The Substring() method extracts a portion of the string starting from a specified index. Optionally, you can specify the length of the substring.

string title = "Introduction to Computer Science";
Console.WriteLine(title.Substring(16, 8));  // "Computer"

Combining IndexOf() with Substring()

You can use IndexOf() to find the starting position of a substring and then use Substring() to extract it.

string name = "Ms Robinson";
int charPos = name.IndexOf("R"); // Finds the position of 'R'
string lastName = name.Substring(charPos);
Console.WriteLine(lastName);     // "Robinson"

Splitting a String

The Split() method breaks a string into an array of substrings based on a specified delimiter.

string teams = "Arsenal,Chelsea,Everton,Liverpool";
string[] teamsArray = teams.Split(',');

foreach (string team in teamsArray)
{
    Console.WriteLine(team);
}
// OUTPUT:
// Arsenal
// Chelsea
// Everton
// Liverpool

Note

If you need to split a string on multiple delimiters or with more complex logic, use Regex.Split().

Replacing a Substring

The Replace() method substitutes all occurrences of a specified substring with another substring.

string message = "Hi John";
string newMessage = message.Replace("John", "Imran");
Console.WriteLine(newMessage);  // "Hi Imran"

Replace() is case-sensitive. Use it carefully when replacing text in a case-insensitive context.

Escaping Characters in a String

Strings must be enclosed in double quotes ("). To include special characters, use escape sequences:

string message = "Hello, my name is \"Khalid\" and I am from London";
Console.WriteLine(message);  // Hello, my name is "Khalid" and I am from London

Common Escape Characters

Escape Character	Result	Description
\\'	'	Single quote
\\"	"	Double quote
\\\\	\	Backslash
\\n	New Line	Moves cursor to the beginning of the next line
\\t	Tab	Inserts a tab space
\\b	Backspace	Moves cursor back one space

Use escape sequences to handle characters like quotes and backslashes within your strings.

Empty String

There are two equivalent ways to initialize an empty string in C#:

string myString1 = String.Empty; // More readable and common
string myString2 = "";           // Equivalent to String.Empty

if (myString1 == String.Empty)
{
    Console.WriteLine("String is empty");
}

Note

string is an alias for System.String. They can be used interchangeably.

Summary

• C# provides a rich set of string methods for common operations like comparison, concatenation, and modification.
• Be aware of case sensitivity when using methods like Equals(), IndexOf(), and Replace().
• Use escape sequences to handle special characters within strings.
• For complex string manipulation, consider using classes like StringBuilder for better performance.