encryption!

[encon]

i have an assignment which asks me to write a program which reads in a text file and encrypts only the letters, and the output reads 13 letters out-of-sync and is also case sensitive.

I have an idea that it should be done using the ascii table but have no idea how to filter out the non-letters or even how to write the code itself,HELP!!!

[Scipio]

Using ASCII codes should work:

http://www.cplusplus.com/doc/ascii.html

The capital letters are one sequence, and the small letters to. You could use that to filter out the non-letters; if ( (letter>= 'A' && letter<='Z') || (letter>='a' && letter<='z') ).