typedef struct {
    int n, i, j, counter;
    double percent;
    int **t1, **t2, **res;
    pthread_t *threads;
}tk;

int n2 = t->n * t->n;
for(int i = 0; i < n2; i++) {
    pthread_create(&(t->threads[i]), NULL, solve, (void *) t);
}

for(int i = 0; i < n2; i++) {
    pthread_join(t->threads[i], NULL);

    //it only prints the end result (100%) n2 times
    //printf("%f%%n", t->percent);
}

void *solve(void *ptr) {
pthread_mutex_lock(&mutex);
tk *t;
t = (tk*) ptr;

int sum = 0;

if(t->j == t->n) {
    t->i++;
    t->j = 0;
}

for(int k = 0; k < t->n; k++) {
    sum = sum + t->t1[t->i][k] * t->t2[k][t->j];
}

t->res[t->i][t->j] = sum;
t->j++;

t->counter++;

t->percent = (t->counter * 100) / (t->n * t->n);

pthread_mutex_unlock(&mutex);