Throw darts at a square of size 1. Count those that land in an inscribed
circle of radius 1/2 and center (1/2, 1/2).  The area of the circle is
pi/4 and the areas of the square is one so the ratio of the hits in the circle
to the total number of trials is pi/4/1 which is pi/4.  Multiply that ratio by
4 to get an estimate of pi.  Use random numbers to throw darts. The rand
function returns arandom number between 0.0 and 1.0.