#include <stdio.h>
#include <stdlib.h>
#include <cstring>
using namespace std;

void dollars(char ** dest, char const *src)
{
    int n = strlen(src);
    int lg = n + 2 + (n-1) / 3;
    *dest = (char*)malloc((lg+1) * sizeof(char));
    (*dest)[0] = '$';
    int k = 1;
    for(int i = 0; i < n; i++)
    {
        (*dest)[k] = src[i];
        k++;


        if(i <= 2)
        {
            if(i+1 == (n-2) % 3)
            {
                (*dest)[k] = ',';
                k++;
            }
        }
        else
        {

        }
    }
    (*dest)[lg] = '\0';
}

int main()
{
    char * x;
    dollars(&x, "123456789");
    printf("%s", x);
    return 0;
}