Manipulating strings is probably the most performed task in programming yet most developer are not doing it efficiently. Developers tend to use the ‘+’ operand to concatenate strings because it is an easy syntax and they are not aware of better options.

In C#, use System.Text.StringBuilder

Make it a habit to use StringBuilder to manipulate strings because the class is designed to be compiler-optimised and it will avoid memory allocation where possible.

String is immutable

Do you know that String type is immutable, which means that it cannot be changed after instantiated. Every time you modify an existing string, a new string is created. Now imagine if you have a loop which append to a string, the .NET runtime have to allocate memory for a new string every time the string is modified. Memory allocation is an expensive operation.

StringBuilder is mutable and optimised

To overcome the resource penalty when manipulating string during runtime, StringBuilder is introduced. It’s operation is compiler optimised and mutable where possible.

When to use StringBuilder?

Understanding the need for easy syntax and readability, I would suggest using StringBuilder whenever you are manipulating string in a loop and performance matters.

For more reading

Namespace System.Text.StringBuilder.aspx)

StringBuilder Benchmark