Ceaser Shift Encryption

I was just wondering if someone could help:

I have a task where the user enters a message and an encryption key (between 1-10).

The program then needs to encrypt the message using the key, and this needs to be done by getting the ASCII value and then adding on the key to the value to get the shift number. The number then needs to be transformed into a character and then repeated for each character to form a new encrypted message string.

eg:
Message - "fire"
Encryption Key - 2 (each character will be shifted along by 2, ie. f becomes h)
Encrypted message - hktg

I cant seem to figure this out, can someone please help.

Cheers.