#include <iostream>
#include <cstring>
 
using namespace std;
 
void cHash(const char* in, char* out) {
    const char allowed_chars[] = "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz";
    const int allowed_len = strlen(allowed_chars);
    const int inlen = strlen(in);
    char last = 254;
    for (int i=0; i<inlen; i++) {
        char c = in[i];
        out[i] = allowed_chars[(c+last) % allowed_len];
        last = c;
    }
}
 
int main() {
    char buffer[] = "Hello world!";
    char* next = (char*) malloc(strlen(buffer)*sizeof(char));
    cHash(buffer, next);
    cout << next << endl;
    free(next);
    return 0;
}