\n\r w/o ungetc

bool checknext = false;
while ((ch = fgetc (infile)) != EOF) {
    if (checknext && ch != '\r') {
        fputc ('\r', outfile);
    }
    fputc (ch, outfile);
    checknext = ch == '\n';
}

if (checknext) {
    fputc ('\r', outfile);
}