个十百千不同，所以可以加入层级判断！

#include<iostream>
#include<string>

using namespace std;

int main()
{
    unsigned n;
    string out;

    cin >> n;

    if (n > 0)
    {
        unsigned a = n % 10;
        for (int i = 1; i <= a; ++i)
        {
            out = out + to_string(i);
        }
        n = n / 10;
        if (n > 0)
        {
            unsigned b = n % 10;
            for (int i = 0; i < b; ++i)
            {
                out = string("S") + out;
            }
        }
        n = n / 10;
        if (n > 0)
        {
            unsigned c = n % 10;
            for (int i = 0; i < c; ++i)
            {
                out = string("B") + out;
            }
        }
    }
    cout << out;


    system("pause");
    return 0;
}