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

#define BUF 64

typedef struct {
    char data[BUF];
    unsigned checksum;
} Packet;

unsigned compute_cs(const char *d) {
    unsigned s = 0;
    for (int i = 0; d[i]; i++) s += (unsigned char)d[i];
    return s;
}

int main(void) {
    Packet p;
    strcpy(p.data, "hello");
    p.checksum = compute_cs(p.data);
    printf("Client: sending '%s' cs=%u\n", p.data, p.checksum);
    for (int try = 1; try <= 2; try++) {
        printf("Try %d: ", try);
        if (try == 1) {
            printf("lost\n");
            continue;
        }
        printf("ok\n");
        unsigned rcs = compute_cs(p.data);
        if (rcs == p.checksum) {
            printf("Server: got '%s' ok, reply 'ack'\n", p.data);
        }
    }
    return 0;
}