.NET API Docs

System.String

The System.String class represents text as a sequence of Unicode characters. It provides a rich set of methods for manipulating, searching, comparing, and formatting strings.

Namespace

System

Assembly

System.Runtime.dll

Inheritance

System.Object → System.String

Immutability

Instances of String are immutable; any operation that appears to modify a string actually creates a new instance.

Common Methods

MethodSignatureDescription
Concat static string Concat(params string[] values) Combines one or more strings into a single string.
Contains bool Contains(string value, StringComparison comparisonType = StringComparison.CurrentCulture) Determines whether the string contains a specified substring.
IndexOf int IndexOf(string value, int startIndex = 0, StringComparison comparisonType = StringComparison.CurrentCulture) Returns the zero-based index of the first occurrence of a specified substring.
Replace string Replace(string oldValue, string newValue, StringComparison comparisonType = StringComparison.CurrentCulture) Returns a new string in which all occurrences of a specified string are replaced.
Split string[] Split(params char[] separator) Splits a string into substrings based on separator characters.
ToUpper string ToUpper(CultureInfo culture = null) Converts the string to uppercase using culture-specific rules.
ToLower string ToLower(CultureInfo culture = null) Converts the string to lowercase using culture-specific rules.
Trim string Trim(params char[] trimChars) Removes all leading and trailing white-space characters from the string.

Key Properties

PropertyTypeDescription
Length int Gets the number of characters in the current string.
Chars char Gets the character at the specified index.

Example: Building a CSV line

using System;
using System.Text;

class Program
{
    static void Main()
    {
        var values = new[] { "Alice", "Bob", "Charlie" };
        var csv = string.Join(",", values);
        Console.WriteLine(csv); // Output: Alice,Bob,Charlie
    }
}

Example: Case‑insensitive search

string text = "Hello World";
bool contains = text.Contains("hello", StringComparison.OrdinalIgnoreCase);
Console.WriteLine(contains); // True