ex_3-3.c

   1 #include <stdio.h>
   2
   3 /* get next group of tokens from stdin */
   4 int get_tokens(int *dir, char *start, char *stop){
   5
   6         int status = 0;
   7         char c = '\0';
   8         if((c = getchar()) != EOF) { ++status; }
   9
  10         if(c == '-') {
  11                 *dir = 1;
  12                 if((*start = getchar()) != EOF) { ++status; }
  13                 if(getchar() != EOF) { ++status; } // should be a '-'
  14                 if((*stop = getchar()) != EOF) { ++status; }
  15         } else {
  16                 *dir = 0;
  17                 *start = c;
  18                 if(getchar() != EOF) { ++status; } // should be a '-'
  19                 if((*stop = getchar()) != EOF) { ++status; }
  20         }
  21
  22         if(status == 4 && *dir == 1) { return 1; }
  23         if(status == 3 && *dir == 0) { return 1; }
  24         return -1;
  25 }
  26
  27 /*
  28
  29 print out series of chars based on spec.
  30 dir = direction to print
  31 start and stop are chars in ASCII to begin and end with.
  32
  33 */
  34 void print_tokens(int *dir, char *start, char *stop)
  35 {
  36         if(*dir == 0){ // foreward
  37                 while(*start != *stop + 1)
  38                 {
  39                         putchar(*start);
  40                         *start = *start + 1;
  41                 }
  42          } else { // reverse
  43
  44                 while(*start != *stop - 1)
  45                 {
  46                         putchar(*start);
  47                         *start = *start - 1;
  48                 }
  49         }
  50 }
  51
  52 int main()
  53 {
  54         char start, stop;
  55         int dir;
  56
  57         while(get_tokens(&dir, &start, &stop) == 1)
  58         {
  59                 print_tokens(&dir, &start, &stop);
  60                 putchar('\n');
  61         }
  62         return 0;
  63 }