What does {0} mean in String.Format?

Question

E.g. in the following example:

string commandText = string.Format("Select * from {0}", filename);

How does the above work?

Answer 1

{0} is a placeholder for the first object given; in this case that's filename, so it will insert whatever filename evaluates to in place of {0}. Similarly, of course you could use {1} and that would be replaced with the second parameter passed, etc.