How do I make my custom chmod program remove file permissions?

My program can add permissions to a file by typing in lower case letters. How can I make it remove permissions, by using uppercase letters.

20 int main(int argc, char **argv) [ 21 22 int c, i; 23 int fileCount; 24 I/to verify the ownership of a file 25 II check: "man getuid 27 struct stat fileStat; 28 mode t addPermissions0; 30 c-getopt (argc, argv, "u:g:o:U:G:0:"; 31 Icheck: "man getopt" 32 if (c='g'){ for (iz0; i