Why use StringBuilder, and how to search string in Stringbuilder object

Experts,

I've built a string using the StringBuilder as follows;

StringBuilder sb = new StringBuilder();

I then add items to sb  as follows:

 sb.AppendLine(str.ToString());

My questions are:

1. Why is a StringBuilder used, and not -  string += "Some more string";
2. How do I search in a string built using sb - My previous search are done on strings as follows:

int first = sb.IndexOf("silly");

...but the above doesnt work, because sb is a stringbuilder object, and not a string.  Should I just do..

string something = sb.ToString();
int first = sb.IndexOf("silly");

( Im worried the above could cause issues with larger strings).Start Free Trial