Raw Image (GrayScale) Compositor

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
int main(int argc, char **argv) {
  if (argc <= 5) {
    fprintf(
      stderr,
      "usage: %s orig.raw compose1.raw compose2 ... out.raw\n",
      argv[0]);
    return EXIT_FAILURE;
  }
  FILE *in[argc - 2];
  for (int i = 0; i < argc - 2; i++)
    in[i] = fopen(argv[i + 1], "rb");
  FILE *out = fopen(argv[argc - 1], "wb");
  while (true) {
    char *r[argc - 2];
    bool eof = false;
    for (int i = 0; i < argc - 2; i++) {
      if ((fscanf(in[i], "%c", r[i])) == EOF) {
        eof = true;
        break;
      }
    }
    if (eof) break;
    double sum = 0.;
    for (int i = 0; argc - 2; i++) {
      sum += *r[i];
    }
    fprintf(out, "%c", (char) (255 * *r[0] / sum));
  }
  for (int i = 0; i < argc - 2; i++)
    fclose(in[i]);
  fclose(out);
  return EXIT_SUCCESS;
}