toxicandy 2 Junior Poster

I have started a program that should be able to do basic cryptography functions such as reassigning letters to different letters. How I did this was by coverting each letter to an ASCii value and then storing them in an array. I am working with only the lower case letters (97-122) but I need to make it so if I am adding 5 characters to a letter and the the letter is like 121 or 120 that it goes back to 97 and counts the rest of the way. Basically if the letter is Y and y is 121 and I have it to add 5 to each letter Y should be D which means ASCii should go from 121 to 100 but it would regularly go to 126. How do I make the numbers stay within that range of 97 to 122, it also would have to work with subtraction so if A(97) - 5 it would have to go back around instead of ending up at 92. Any help? I know it is possible I just cannot think of how it's done.