How to use StringBuilder wisely?

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Modifying immutable structures like strings must be done by copying the structure, and by that, consuming more memory and slowing the application’s run time (also increasing GC time, etc…).

StringBuilder comes to solve this problem by using the same mutable object for manipulations.

However:

when concatenating a string in compile time as the following:

string myString = "123";
myString += "234";
myString += "345";

it will actually compile to something like that:

string myString = string.Concat("123", "234", "345");

this function is faster than working with StringBuilder for the number of strings entering the function is known.

so for compile-time-known string concatenations you should prefer string.Concat().

as for unknown number of string like in the following case:

string myString = "123";
if (Console.ReadLine() == "a")
{
    myString += "234";
}
myString += "345";

Now the compiler can’t use the string.Concat() function, however, StringBuilder appears to be more efficient in time and memory consumption only when the concatenation is done with 6-7 or more strings.

Bad practice usage:

StringBuilder myString = new StringBuilder("123");
myString.Append("234");
myString.Append("345");

Fine practice usage (note that if is used):

StringBuilder myString = new StringBuilder("123");
if (Console.ReadLine() == "a")
{
    myString.Append("234");
}
myString.Append("345");

Best practice usage (note that while loop is used):

StringBuilder myString = new StringBuilder("123");
while (Console.ReadLine() == "a")
{
    myString.Append("234"); //Average loop times 4~ or more
}
myString.Append("345");

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