For my darling

#include <stdio.h>
#include <stdbool.h>
#include <inttypes.h>

const int num_shift = '9' - '0' + 1;
const int upper_shift = 'Z' - 'A' + 1;
const int min_num = '0';
const int max_num = '9';
const int min_upper = 'A';
const int max_upper = 'Z';
const int min_lower = 'a';
const int max_lower = 'z';

int main() {
    int c = 0;
    uint64_t sets[1000];
    uint64_t current_set = 0;
    int pointer = 0;
    while ((c = getchar()) != EOF) {
        if (c >= min_num && c <= max_num) {
            current_set |= ((uint64_t )1 << (c - min_num));
        } else if (c >= min_upper && c <= max_upper) {
            current_set |= ((uint64_t )1 << (c - min_upper + num_shift));
        } else if (c >= min_lower && c <= max_lower) {
            current_set |= ((uint64_t )1 << (c - min_lower + num_shift + upper_shift));
        } else if (c == '#') {
            current_set = 0;
            sets[pointer] = current_set;
            current_set = 0;
            ++pointer;
        } else if (c == '|') {
            sets[pointer - 2] = sets[pointer - 2] | sets[pointer - 1];
            --pointer;
        } else if (c == '&') {
            sets[pointer - 2] = sets[pointer - 2] & sets[pointer - 1];
            --pointer;
        } else if (c == '~') {
            sets[pointer - 1] = ~sets[pointer - 1];
        } else if (c == '^') {
            sets[pointer - 2] = sets[pointer - 2] ^ sets[pointer - 1];
            --pointer;
        } else {
            if (current_set != 0) {
                sets[pointer] = current_set;
                current_set = 0;
                ++pointer;
            }
        }
    }
    uint64_t res = sets[pointer - 1];
    bool empty = true;
    for (int i = 0; i != 62; ++i) {
        if (i < num_shift) {
            if (res & ((uint64_t)1 << i)) {
                empty = false;
                putchar(min_num + i);
            }
        } else if (i < num_shift + upper_shift) {
            if (res & ((uint64_t)1 << i)) {
                empty = false;
                putchar(min_upper + i - num_shift);
            }
        } else {
            if (res & ((uint64_t)1 << i)) {
                empty = false;
                putchar(min_lower + i - num_shift - upper_shift);
            }
        }
    }
    if (empty) {
        putchar('#');
    }
    putchar('\n');
}