Learning_More

#define _XOPEN_SOURCE 500
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

void printHelp(FILE *stream, char progname[]);

int main(int argc, char *argv[])
{
   char mph[10] = { 0 };
   int opt;
   int cont = 0;

   /* Parse command-line options */
   while ((opt = getopt(argc, argv, "ch")) != -1)
   {
      switch(opt)
      {
         case 'h':
            printHelp(stdout, argv[0]);
            return 0;
         case 'c':
            cont = 1;
            break;
         default:
            printHelp(stderr, argv[0]);
            return 1;
      }
   }

   while(fgets(mph, sizeof(mph), stdin) != NULL)
   {
      /* Check if mph is numeric
       * (and do conversion) */
      if( strspn(mph, "0123456789.-\n") ==
            strlen(mph) )
      {
         printf("%.1f\n", (atof(mph)*1.60934) );
      }
      /* If mph is NOT numeric, print error
       * and return */
      else
      {
         fprintf(stderr, "Found non-numeric "
            "value\n");
         if (cont == 1) /* Check if -c is set */
         {
            continue; /* Skip and continue if
                       * -c is set */
         }
         else
         {
            return 1; /* Abort if -c is not set */
         }
      }
   }
   return 0;
}

void printHelp(FILE *stream, char progname[])
{
   fprintf(stream, "%s [-c] [-h]\n", progname);
   fprintf(stream, " -c continues even though a non"
      "-numeric value was detected in the input\n"
      " -h print help\n");
}

From: https://github.com/PacktPublishing/Linux-System-Programming-Techniques