$ls first-example first-example.c new-sum.c sum sum.c $cat new-sum.c #define _XOPEN_SOURCE 500 #include <stdio.h> #include <stdlib.h> #include <unistd.h> void printhelp(char progname[]); int main(int argc, char *argv[]) { int i, opt, sum; /* Simple sanity check */ if (argc == 1) { printhelp(argv[0]); return 1; } /* Parse command-line options */ while ((opt = getopt(argc, argv, “smh”)) …