int number_of_set_bits(int c) {
    int num = 0;
    if (c)
        do num++; while (c &= c - 1);
    return num;
}
char get_parity_byte(char payload[], int len) {
    parity_t parity = parity_of_string(payload, len);
    switch(parity) {
        case ODD :
            // return 'c';
            return 1;
        case EVEN :
            // return 'p';
            return 0;
        default: return 'c';
    }
}
parity_t parity_of_string(char payload[], int len) {
    // Total number of set bits
    int no_set = 0;
    int i = 0;
    for(i = 0; i < len; i++) {
        no_set += number_of_set_bits(payload[i]);
    }
    return ((no_set % 2) == 0) ? EVEN : ODD;
}
if(strncmp(command, "cp ", 3) == 0) {
            // Opening file
            int file = open(&command[3], O_RDONLY);
            int copiat;
            // Size of file
            int file_size = size(&command[3]);

            // size of file
            sprintf(r.payload, "%d", file_size);
            switch(mode) {
                case 0:
                    r.len = digitsNo(file_size);
                    break;
                case 1:
                    r.payload[0] = get_parity_byte(r.payload, r.len);
                    sprintf(&r.payload[1], "%d", file_size);
                    r.len = digitsNo(file_size) + 1;
                    break;
            }
            printByte(r.payload[0]);
            printf("%s\n",&r.payload[1]);

            send_message_until_ACK(&r, ack_len);

            char *buf;
            int size;
            switch(mode) {
                case 0:
                    buf = (char *) malloc(1400);
                    size = 1400;
                    break;
                case 1:
                    buf = (char *) malloc(1399);
                    size = 1399;
                    break;
            }
            lseek(file, 0, SEEK_SET);
            while ((copiat = read(file, buf, size))) {
                    // Prepare packet
                    r.len = copiat;

                    memcpy(r.payload, buf, size);
                    // Modifying message according to mode
                    switch(mode) {
                        case 1:
                            r.payload[0] = get_parity_byte(buf, copiat);
                            memcpy(&r.payload[1], buf, size);
                            r.len ++;
                            break;
                    }

                    // Send packet
                    send_message_until_ACK(&r, ack_len);
            }
            close(file);
        }