"I am not sure for line 248 if I am doing this correctly"
Rather than concatenating together using [] you should use fullfile:
"Also would you happen to know what the % in sprintf means."
By itself, not much. But when combined with other characters it tells sprintf (and fprintf) how to represent the input data as text. In your code the format specifier %04d will print an integer value with four digits, using leading zeros if required. Format specifiers are explained here:
