Division in loop

hi all,

....
int fd, fdp;
unsigned int size;
int progress = 0;
size_t bytes = 0;
void *buffer;
....

/* open fd from a device then create fdp, allocate buffer,, etc. */

while (bytes < size) {
        ret = read(fd, buffer + bytes, size - bytes);
        if (ret == -1) {
            perror("read");
            return -1;
        }
        ret = write(fdp, buffer + bytes, ret);
        if (ret == -1) {
            perror("write");
            return -1;
        }
        bytes += ret;

        progress = (int) ((bytes / size) * 100);
        printf("\rcompleted: %i%%", progress);
        fflush(stdout);
    }

....

I run this loop to receive some data, the printf() seem not updated,
the progress output is
always in it's initial value until the loop was finished. but when i do...

progress = (int) ((bytes / 2) * 100); /* change size to 2 (or random number) */

then it's works... what's wrong here???