C# `String.CompareTo()`: Performing Lexicographical String Comparisons

Learn how to use C#'s `String.CompareTo()` method for comparing strings and determining their lexicographical order. This tutorial explains its functionality, different overloads, return values, and demonstrates its usage in various string comparison and sorting scenarios.

Understanding C#'s `CompareTo()` Method for Strings

The C# `CompareTo()` method compares a string instance with another string, determining their relative order based on lexicographical sorting. It's a fundamental method for string manipulation and comparison.

`CompareTo()` Method Signatures

The `CompareTo()` method has two versions:

• public int CompareTo(string str): Compares the current string instance with the specified string (`str`).
• public int CompareTo(object obj): Compares the current string instance with another object. The object must be a string; otherwise, it will throw an exception.

Parameters

The first version takes a string as a parameter. The second version takes an object that must be a string; otherwise, an exception is thrown.

Return Value

The method returns an integer:

• 0: The two strings are equal.
• Positive Number: The current string instance comes *after* the specified string in lexicographical order.
• Negative Number: The current string instance comes *before* the specified string in lexicographical order.

Example

using System;

public class StringExample {
    public static void Main(string[] args) {
        string str1 = "apple";
        string str2 = "apple";
        string str3 = "banana";
        Console.WriteLine(str1.CompareTo(str2)); // Output: 0
        Console.WriteLine(str1.CompareTo(str3)); // Output: -1
    }
}

This example demonstrates comparing two strings using `CompareTo()`. The output shows that "apple" is equal to "apple" (0), and "apple" comes before "banana" (-1).