如何在NSString中获取单词或音节的索引

i need to get location(index) of word or syllable of NSString. I'm sorry about i can't post any code because i have no idea where to start. I m working with web service and service will be back to me word or syllable in sentence and will tell me any color and i have to change color of word in sentence. I figured this out how to change color of character but i need to know index of it. I will be really thankful for any clue or help. Thanks in advance.i need to get location(index) of word or syllab