This example is found in the C++ Annotations, available from

                      http://www.icce.rug.nl/documents/

The example defines a calculator accepting mixed-expressions (int and double
operands). It focuses on the mixed-type operands, and converts the expressions
to Reversed Polish Notation (HP-calculator type) expressions. Only the +, the
*, the unary - and nested expressions are implemented. 

Expression values are printed as cut-off integral values. Internally,
double-arithmetic is used.

Enter one expression per line. 

Error recovery is provided by skipping all information on one line when a
syntax error is encountered.

Enter an empty line to terminate the program.

