My work

#include "stdafx.h"
#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <conio.h>
#include <vector>
#include <string>

using namespace std;

void order(char x[], int n) //упорядочивание символов
{
    for (int i(0); i < n - 1; i++)
    {
        for (int j(i + 1); j < n; j++)
            if (x[i] > x[j])
                swap(x[i], x[j]);
    }
}

int engine_func(char *alphabet, size_t length, const size_t last_digit)
{
    vector<size_t> number(length, 0); // indices into alphabet
    for (; ; )
    {
        // print number
        for (auto i : number) cout << alphabet[i];
        cout << '\n';

        // increment the rightmost digit
        size_t pos = length;
        while (number[--pos] == last_digit)
        { // overflow
            if (pos == 0)
            {
                return 0; // no more digits
            }
            number[pos] = 0; // set to zero and increment the left neigbor
        }
        ++number[pos];
    }
}

int main(int argc, char* argv[])
{
    cout << "3n73r y0ur k3ys: ";
    char alphabet[50]; //входное слово
    char x;
    int alph_len(0); // для запоминания размера массива
    cin >> x;
    while (x != '/')
    {
        alphabet[alph_len] = x;
        alph_len++;
        cin >> x;
    }
    alphabet[alph_len] = '\0';
    order(alphabet, alph_len);

    const size_t last_digit = alph_len - 1; // '\0'
    //const size_t length = 6;
    const size_t min_length = 4;
    const size_t MIN = argc > 1 ? stoul(argv[1]) : 4;
    const size_t length = argc > 1 ? stoul(argv[2]) : 10;

    int a;
    for (size_t len = MIN; len < length; len++)
    {
        a = engine_func(alphabet, len, last_digit);
    }

    _getch();
    return a;
}