I am doing the substitution question and I keep running into this segmentation fault issue but i do not understand what exactly is causing the memory access issue. once j=4, the memory fails to be accessed for that particular character in the cipher key. the printf is for debugging, so that i can see where the conversion is failing. the numbers are all correct for the first 4 characters but I do not know why the 5th character is giving memory problems, for other cipher keys as well. thank you for your help!