file-enc.c improved

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

int main(int argc, char **argv){
    FILE *in,
         *out;
    char *key;
    int c,
        len;

    if(argc != 4){
        printf("Usage: %s [input file] [output file] [encryption key]", *argv);
        return 1;
    }

    in  = fopen(argv[1], "r");
    out = fopen(argv[2], "w");
    key = argv[3];
    len = strlen(key);

    while( (c = fgetc(in)) != EOF){
        fputc(c ^ *key, out);
        key = key == argv[3] + len ? argv[3] : key + 1;
    }

    fclose(in);
    fclose(out);
    return 0;
}