Well this is my first post on the forum. Been browsing the site for some days but i need some quick help so figured, why not go here?

Well im pretty new to this whole programming thing, although ive made a few programs. My pride and joy is a program to handle prime numbers. You set up an interval of your choosing and then the program will find all the prime numbers in the interval. You can input a single number within the interval and the program will then find the neares prime number above and below. You can output a complete list of the primes in the interval and save them in a file... and i think also some other stuff...

The point is that i know a little but i dont realy know anything about ASCII. Not true, i know what it is but i dont know how to work with it. Im trying to make a simple encryption and decryption program where the ASCII values are changed. I.e. five is added so that "a" (97) becomes "f" (102) but i have no idea on how do actualy do this. I hope some of you guys in here can help me?