Strings are immutable types in .NET. Whenever you modify a String object in .NET, a new String object is created in memory to hold the new data. By contrast, a StringBuilder object represents a mutable string of characters, and expands its memory allocation dynamically as the size of the string grows.
The String and StringBuilder classes are two popular classes that you will use frequently when working with strings in .NET Framework and in .NET Core. However, each has its benefits and downsides.
