rot13 example

#include <stdio.h>                                                                                                                             
#include <string.h>
#include <malloc.h>

char * rot(const char *origStr, int shift) {
   char *newStr = (char*)malloc(strlen(origStr) + 1);
   int i = 0;
   while(origStr[i]) {
      if('a' <= origStr[i]  && origStr[i] <= 'z') {
         newStr[i] = (origStr[i] - 'a' + shift)%26 + 'a';
      } else if('A' <= origStr[i]  && origStr[i] <= 'Z') {
         newStr[i] = (origStr[i] - 'A' + shift)%26 + 'A';
      } else {
         newStr[i] = origStr[i];
      }
      i++;
   }
   newStr[i] = '\0';
   return newStr;
}

int main(int argc, char**argv) {
   int shift = 13;
   size_t nbytes = 80;
   char *str = (char *) malloc (nbytes + 1);

   if(argc > 1) {
      int i;
      for(i = 1; i < argc; i++) {
         char *rotStr = rot(argv[i], shift);
         printf("%s\n", rotStr);
         free(rotStr);
      }
   } else {
      int bytes_read = 0;
      do {
         bytes_read = getline (&str, &nbytes, stdin);
         char *rotStr = rot(str, shift);
         printf("%s", rotStr);
         free(rotStr);
      } while (bytes_read > 0);
   }

   return 0;
}