Shift damn you.

So, im writing a c++ program and i have it all done encept for some reason i cannot get the idea behind shifting a string down.
so i was wondering how you code to get
abc...yz   to become
bcd...za?

...thanks
now accepting that i am ignorant and forever a tard i am going to ask if i can get some clarity on the subject and yes it is a Caesar cipher i am trying to program for.