J1. Interested in (do)ing and interested to (do)
a. I'm interested in doing something = I'm thinking of doing it, I would like to do it. (e.g. Let me know if you're interested in joining the club. (not to join))
b. use interested to ~ to say how somebody reacts to what they hear/ see/ read/ learn/ know/ find: I was interested to hear it = I heard it and it was interesting for me. (e.g. I was interested to hear that Tanya has left her job.)
c. This structure is the same as surprised to ~/ glad to ~ etc. (e.g. I was surprised to hear that Tanya has left her job.)
more about the To ~ (Infinitive) and preposition + Gerund (-ing)
Idiom 365
Raining Cats and Dogs: A very loud and noisy rain storm
Example: Sometime you can say cats and dogs when it is raining heavily.