random number generator not working properly

[SwissPie]

I'm trying to generate random social security numbers from 000 - 00 - 0000 to 999 - 99 - 9999 , so what I did was generate a random number from 0 to 999999999, convert the int to a string, and then add leading zero if it wasn't a 9 digit number, and then added a '-'. However, after I set the width to 9 and added the leading zeros, my program will not generate anything in the first four digits.

#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
using namespace std;

 int rng11(){return 1+(rand()%999999999);}

int main()
{
    srand(time(NULL));
    string student[100];
    for (int i=0; i<100; i++)
    {
        int z = rng11();
        string result;
        stringstream convert;
        convert  << std::setw(9) << setfill('0') << z ;
        result = convert.str();
        result.insert(3,1, '-');
        result.insert(6,1, '-');
        student[i] = result;
        cout << student[i] << endl;
    }

    return 0;
}

[Repeater]

rand() generates a random number between zero and RAND_MAX.

RAND_MAX could be as low as 32767.

If you never see a number above 000099999 , it suggests your RAND_MAX is less than 100000.

rand() is bad. Don't use rand().
https://channel9.msdn.com/Events/GoingNative/2013/rand-Considered-Harmful

Here is a better, C++11 random number generator: https://www.guyrutenberg.com/2014/05/03/c-mt19937-example/

Don't use modulus to trim your random numbers to a range you want. That makes them much, much less random.

Try something like:
mt19937::result_type seed = time(0);
and then to get your numbers:

auto dice_rand = std::bind(std::uniform_int_distribution<int>(0,999999999),
                           mt19937(seed));