[c-prog] geometric mean

[Bill Cunningham]

 double Sma(double *nums, int n)
{
    double total = 0;
    int i;
    for (i = 0; i < n; i++)
        total += nums[i];
    return total / n;
}

I want to take this function a step further and have it calculate a 
geometric mean. But I have no idea where to start. Any ideas?

Bill