Assign Scores To Separate Strings In An Array?

I was working on this problem that asks me to return an array of scores for each string (only for its content part, not URL) in the global variable, which is an array. For example, alert a score of 0 if the string z is not found, 1 if found once, and 2 for twice. My problem is that I can get the code to alert if it has found the word (ex. "the"), but I cannot manage to :

a) Assign separate scores for each string.

b) Make the search case insensitive i.e. "the" will appear in 0,1, but not in 2, where it is capitalized

[CODE]
var c = ["[www.facebook.com] Facebook is the best social networking site to coccent with your friends. ", "[www.google.co.uk] Google is the worldwide search engine. ", "[www.bbc.co.uk] The best news source for starting your day. "];
function findScore(z) {

[Code]...