Difference between string and StringBuilder in C#

A key difference is that string is immutable. This means once a string is created, it cannot be changed.

For instance, when you modify a string, a new object is created in memory instead of altering the original one. If you have a string "Hello" and change it to "Hello, World!", it creates a new string object rather than modifying the original "Hello" string.

For example:

string message = "Hello";
message += ", World!"; // creates a new string object

In contrast, StringBuilder is mutable, meaning you can modify its value without generating a new object each time. When you append, insert, or remove characters from a StringBuilder, it modifies the existing object, which leads to better performance, especially when performing many operations on the string.

For example:

StringBuilder sb = new StringBuilder("Hello");
sb.Append(", World!"); // appends to the same object

The performance difference becomes especially noticeable when you modify the text repeatedly. If you are performing many operations (like concatenation or insertions) on a string, it is more efficient to use StringBuilder.

If you are modifying a string more than five times, you should prefer StringBuilder to avoid unnecessary object creation and improve efficiency.