H1: lex/yacc

Assignment: Calculator

In this homework you will create a simple calculator (see calc.ebnf). This must be done with lex and yacc. Skeleton files are provided here. You may notice that Makefile is set up for using C++, which means you can use STL to make your life easier (hopefully).

Description:

The specific goal of this assignment is to familiarize yourself with lex and yacc. As a result of this assignment you should know and be able to explain the principles of lex/yacc, how they interface and the following items: conflicts in yacc, yyin, yytext, yyleng, yylex(), yywrap(), yymore(), yyless(), yyparse(), yyerror(), yychar, yydebug. Another question: what does -ly argument to cc command do?

The 'calc' program usage is: calc [filename]. Without a filename argument it reads from stdin. It should gracefully exit after reaching the end of file. The command 'quit' exits the program.

The calculator needs to understand two types of statements: expression evaluation (e.g. 2*2), and setting variables (e.g. set pi 3.1415926535). When an expression is evaluated, the result is printed using

printf("%g\n",expr);

Here's a sample calculator session:

> calc
2*2
4
set a 5*5
a
25
sqrt(a)
5
quit
>

Your calculator should understand integers and standard C floating point constants, e.g. 2.718281828459045, 6.022e23, etc. A valid floating point constant consists of a non-empty sequence of digits optionally containing a radix character, then an optional exponent part. An exponent part consists of e or E, followed by an optional sign, followed by one or more decimal digits. You do not need to implement high precision operations. Regular 'double' precision operations will do. Do not do anything special with regard to overflow.

Turnin:

Copy all your source files, including a Makefile, to your turnin directory by the specified time. Do not include binaries or object files. The sample Makefile has a target 'turnin', so that when you are done, all you need to do is 'make turnin' (unless your project is different from the assumptions in the Makefile). There must not be any conflicts in your yacc specification.

Useful links:

docs.sun.com: Programming Utilities Guide (Besides good documentation on lex, yacc and other utilities, there's a description of a simple desk caclulator which might be somewhat useful for this assignment.)

vin@nd.edu

Last modified: Wed Jan 16 16:50:31 EST 2002