A C++ class for histogramming data

Another recurring issue; How to effectively create a histogram of some data? A histogram is also called a frequency distribution.

I have created a small class in C++ that provides a histogram and can count the frequency of data values within a range. The code is supplied below for your amusement. If you have any idea on how to improve on the code, please let me know in a comment. Of course, the standard template library could be used, e.g. std::vector<unsigned int>, if you like to have an even more simple class. But I like code that have no includes :-)

Update 2011-06-17: I added code to keep track of overflows, i.e. counting the number off calls to the Add method with an argument that would not fit in the histogram range.

Update 2011-08-03: Added track of underflows, similar to the overflow addition 2011-06-17.

// A histogram class.
// The Histogram object can keep a tally of values
// within a range, the range is arranged into some
// number of bins specified during construction.
// Any allocation of a Histogram object may throw
// a bad_alloc exception.
// Dedicated to the public domain.
// Jansson Consulting
// 2009-06-30, updated 2011-06-17 and 2011-08-03
class Histogram
{
   public:
      // Construct a histogram that can count
      // within a range of values.
      // All bins of the histogram are set to zero.
      Histogram(
            const double& Start,
            const double& End,
            const unsigned int& nBins):
         Start(Start),
         nBins_by_interval(nBins/(End-Start)),
         nBins(nBins),
         freq( new unsigned int[nBins] ),
         overflow(0U),
         underflow(0U)
      {
         for(unsigned int i(0); i < nBins; ++i)
            freq[i] = 0U;
      }
      // Construct a histogram by copying another one.
      Histogram(const Histogram& other):
         Start(other.Start),
         nBins_by_interval(other.nBins_by_interval),
         nBins(other.nBins),
         freq( new unsigned int[nBins] ),
         overflow(other.overflow),
         underflow(other.underflow)
      {
         for(unsigned int i(0); i < nBins; ++i)
            freq[i] = other.freq[i];
      }
      // Deallocate the memory that was allocated for
      // the tallied counts.
      ~Histogram() {delete[] freq;}
      // Set this histogram equal to another.
      Histogram& operator=(const Histogram& other)
      {
         if( this != &other )
         {
            Start = other.Start;
            nBins_by_interval = other.nBins_by_interval;
            if( nBins != other.nBins )
            {
               nBins = other.nBins;
               delete[] freq;
               freq = new unsigned int[nBins];
            }
            for(unsigned int i(0); i < nBins; ++i)
               freq[i] = other.freq[i];
            overflow = other.overflow;
            underflow = other.underflow;
         }
         return *this;
      }
      // Increase the count for the bin that holds a
      // value that is in range for this histogram or
      // the under-/overflow count if it is not in range.
      void Add(const double& x)
      {
         if( x < Start )
            underflow++;
         else
         {
            const unsigned int i(
                  static_cast<unsigned int>(
                     (x-Start)*nBins_by_interval) );
            if( i < nBins ) freq[i]++;
            else overflow++;
         }
      }
      // Get the sum of all counts in the histogram.
      unsigned int GetTotalCount() const
      {
         unsigned int c(0U);
         for( unsigned int i(0); i < nBins; ++i )
            c += freq[i];
         return c;
      }
      // Get the overflow count.
      unsigned int GetOverflow() const
      {
         return overflow;
      }
      // Get the underflow count.
      unsigned int GetUnderflow() const
      {
         return underflow;
      }
   private:
      double Start,nBins_by_interval;
      unsigned int nBins;
      unsigned int* freq;
      unsigned int overflow;
      unsigned int underflow;
};