String vs. StringBuilder

Question

I understand the difference between String and StringBuilder (StringBuilder being mutable) but is there a large performance difference

Answer 1

StringBuilder reduces the number of allocations and assignments, at a cost of extra memory used. Used properly, it can completely remove the need for the compiler to allocate larger and larger strings over and over until the result is found.

string result = "";
for(int i = 0; i != N; ++i)
{
   result = result + i.ToString();   // allocates a new string, then assigns it to result, which gets repeated N times
}

vs.

String result;
StringBuilder sb = new StringBuilder(10000);   // create a buffer of 10k
for(int i = 0; i != N; ++i)
{
   sb.Append(i.ToString());          // fill the buffer, resizing if it overflows the buffer
}

result = sb.ToString();   // assigns once