randgen.h

#ifndef _RANDGEN_H
#define _RANDGEN_H

// RandGen objects provide a source of computer-generated random numbers
// (sometimes known as pseudo-random numbers).  
//
// By default, a RandGen object will produce a different series of
// numbers (through repeated calls to the RandInt and RandDouble
// methods) every time the program is run.  When testing, though, it is
// often useful to have a program generate the same sequence of numbers
// each time it is run; this can be achieved by specifying a "seed" when
// the first RandGen object in the program is created.
//
// To construct random integers in a given range, client programs
// should use RandInt.  To construct random doubles, client programs
// should use RandReal.  The ranges for the return values for these
// functions are indicated with mathematical notation:
//    [0..max)     means a number between 0 and max,
//                 not including max but including 0;
//    [0..max]     means a number between 0 and max, including
//                 both 0 and max.
//
// For example,
//    RandGen r;
//    r.RandInt(5)         an int between 0 and 5, not including 5
//    r.RandInt(0, 5)      an int between 0 and 5, might include 0 or 5
//    r.RandReal()         a double between 0 and 1, not including 1
//    r.RandReal(4, 6)     a double between 4 and 6, might include 4 or 6
//
// Technical Note:
//   The "seed" used by all random number generation in a program is set
//   the first time a random number generator object is constructed by
//   the program.  All other random number generator objects created
//   later in the program will use the same seed.

class RandGen
{
  public:

    // Constructors
      // If the first RandGen object is constructed with the default
      // constructor, a different series of numbers is produced every
      // time the program is run.  If the first RandGen object is
      // constructed with a seed, the same series of numbers is produced
      // every time.

    RandGen();                          // default constructor
    RandGen(int seed);                  // produce same series every time
                                        //   (most useful during testing)    

    // Accessing functions
      // Ranges for return values are indicated with mathematical
      // notation:
      //    [0..max)     means a number between 0 and max,
      //                 not including max but including 0;
      //    [0..max]     means a number between 0 and max, including
      //                 both 0 and max.

    int RandInt(int max);                  // returns int in [0..max)
    int RandInt(int low, int max);         // returns int in [low..max]
    double RandReal();                     // returns double in [0..1)
    double RandReal(double low, double max); // returns double in 
                                             // [low..max]

  private:
    static int ourInitialized;        // for 'per-class' initialization
};

#endif    // _RANDGEN_H not defined