Need help with generating random numbers

I need to generate random numbers between 100 and 999
this is what i got but this doesn't work every time. It goes over 999 sometimes


#include <iostream>
#include <cstdlib>
#include <ctime>

using namespace std;

int main()
{
int num;
int count = 1;
unsigned seed = time(0);

srand(seed);

while(count <= 20)
{
num = 100 + rand() % 999;
cout << num << endl;
count++;
}
}

try this, num = 100 + rand() % 899;