Interactive search/replace regex in Vim?

Question

I know the regex for doing a global replace,

     %s/old/new/g

How do you go about doing an interactive search-replace in Vim?

Answer 1

Mark Biek pointed out using:

%s/old/new/gc

for a global search replace with confirmation for each substitution. But, I also enjoy interactively verifying that the old text will match correctly. I first do a search with a regex, then I reuse that pattern:

/old.pattern.to.match
%s//replacement/gc

The s// will use the last search pattern.