XOR Encryption

#include <stdio.h>
#include <stdlib.h>

FILE * input,
     * key,
     * output;

int main(void) {
  input  = fopen("in.txt",  "r");
  key    = fopen("key.txt", "r");
  output = fopen("out.txt", "w");
  
  if(!input)  { puts("input failure");  return EXIT_FAILURE; }
  if(!key)    { puts("key failure");    return EXIT_FAILURE; }
  if(!output) { puts("output failure"); return EXIT_FAILURE; }
  
  while(!feof(input))
    { if(feof(key)) rewind(key); fputc(fgetc(input) ^ fgetc(key), output); }
  
  return EXIT_SUCCESS;
}