Limiting double to 3 decimal places

Question

This i what I am trying to achieve:

If a double has more than 3 decimal places, I want to truncate any decimal places beyond the third. (do not round.)

Answer 1

In C lang:

double truncKeepDecimalPlaces(double value, int numDecimals)
{
    int x = pow(10, numDecimals);
    return (double)trunc(value * x) / x;
}