Ceasar cipher encryption problem

hello every one , i have an assignment to write a code for Ceasar cipher for the following set of alphabet { 0,1,2,3,4,5,6,7,8,9,A,B,D,....,Z ,a,b,c,d,....,z} the problem is the ASCII code have different values , for example if i shift number "9" to "A" then 57 to 65 should be shifted is there any suggestion how do i solve this problem? is there any way i can assign values to the letters (changing ASCII values)?