You're storing the same character every time. Seems to me like you want to modify the value of the character each time through the loop.
If you want to store P to A, then you probably want another loop that starts with P and decrements the value.
PLEASE USE CODE TAGS (the <> formatting button) when posting code. http://v2.cplusplus.com/articles/jEywvCM9/
It makes it easier to read your code and it also makes it easier to respond to your post.