C# / .NET - replace last 3 characters in string

In this article, we would like to show you how to replace the last 3 characters in a string in C#.

Quick solution: 

string originalString = "ABCDE";

string replaced = originalString.Substring(0, originalString.Length - 3) + "123";

Console.WriteLine(originalString); // ABCDE
Console.WriteLine(replaced);       // AB123

Practical examples

1. Using Substring() method

using System;

public class Program
{
    static string ReplaceLastLetters(string text, int letterCount, string newLetters)
    {
        string substring = text.Substring(0, text.Length - letterCount); // ABCDE -> AB
        return substring + newLetters;
    }

    public static void Main(string[] args)
    {
        string originalString = "ABCDE";
        string newLetters = "123";

        string replaced = ReplaceLastLetters(originalString, 3, newLetters);

        Console.WriteLine(originalString); // ABCDE
        Console.WriteLine(replaced);       // AB123
    }
}

Output:

ABCDE
AB123

1. Using Remove() method

using System;

public class Program
{
    static string ReplaceLastLetters(string text, int letterCount, string newLetters)
    {
        string substring = text.Remove(text.Length - letterCount, letterCount); // ABCDE -> AB
        return substring + newLetters;
    }

    public static void Main(string[] args)
    {
        string originalString = "ABCDE";
        string newLetters = "123";

        string replaced = ReplaceLastLetters(originalString, 3, newLetters);

        Console.WriteLine(originalString); // ABCDE
        Console.WriteLine(replaced);       // AB123
    }
}

Output:

ABCDE
AB123

 References

1. String Substring() - .NET Docs