COP 3402
Fall 2002
Lab #4 (20 pts - out of a total of 400 points for the course)
Due: Monday, November 18

Note: The general comments at the beginning and end of the previous
      labs apply to this lab as well.  So, you may refer to them to
      refresh your memory about guidelines.

In this program, you will use lex (flex) and yacc (bison) to process
simple assignment statements.

Each assignment statement has the following syntax:
       variable = expression;
Assume that each statement starts on a new line and terminates on the
same line (i.e., it is not across several lines).  Also assume that
all statements are syntactically and semantically correct, i.e., no
error checking.

The variables will be only single upper-case letters, i.e.,
26 variables.

The expressions will contain integers, variables, and three binary
operations: addition (indicated by '+'), min or smaller of two
operands (indicated by '!'), and max or larger of two operands
(indicated by '@').


Addition has precedence over min and max (min and max have the same 
precedence).  Thus, the expression 10 ! 20 + 30 results in 10.

The associativity for all three operations is left-to-right.  Thus,
the expression 10 ! 30 @ 20 results in 20.

Parenthesized expressions have higher precedence, i.e., parentheses
may be used in the expressions to override precedence/associativity.
Thus, the expression (10 ! 20) + 30 results in 40 and the expression
10 ! (30 @ 20) results in 10.

I have provided parts of the yacc (bison) and lex (flex) input below,
but you don't have to use them if you don't want to.

/********************************************************************/

/* lab4.y */

%{

   /* definitions */

#include <ctype.h>

#include <limits.h>  /* INT_MIN is defined in this header file */

#define  LETTERS  "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

char  symbols[27]; /* contains the 26 variable names       */
int   values[26];  /* contains values for the 26 variables */

%}

%start startsym

%token VARIABLE NUMBER

%%

   /* rules */

startsym   : assignlist
           ;

   /*****   YOU DO THE REMAINING RULES!   *****/

%%

   /* user routines */

   main()
   {
      int  k;

      strcpy(symbols, LETTERS);

      /* initialize the variables to a "dummy" value */
      for ( k = 0;   k < 26;   ++k )
         values[k] = INT_MIN;

      /* process the assignment statements */
      yyparse();

      /* print the final values for the variables */
      printf(" Symbol Table \n");
      printf("Symbol   Value \n");
      for ( k = 0;   k < 26;   ++k )
         if ( values[k] != INT_MIN )
            printf("  %c     %5d \n", symbols[k], values[k]);
      
   }/* end of main */

/********************************************************************/

/* lab4.l */

%{

   /* definitions */

#include "lab4.tab.h"

extern char symbols[];

int  findindex();

%}

%%

   /* rules */

[ ]+   {/* skipping blanks */
        ;
       }

   /*****   YOU DO THE REMAINING RULES!   *****/

   If token is a number, the "action" part of the rule should
       set "yylval" to the value of the number and return NUMBER.

   If token is a variable, the "action" part of the rule should
       set "yylval" to the index of the variable and return VARIABLE.

   Other rules should be straightforward!

%%

   /* user routines */

   int findindex(sym)
      /* This routine finds the index for a variable. */
      char  sym;
   {
      int   k;

      for ( k = 0;   k < 26;   ++k )
         if ( symbols[k] == sym )
            return(k);

      printf("*** ERROR: The variable  %c  is not A-Z *** \n", sym);

   }/* end of findindex */

/********************************************************************/

/* Sample lab4.inp */

B = 12;
M = B + 8;
P = 10 @ 30;
Q = B + M @ P;
R = P ! Q;
S = 10 ! 20 + 30;
T = 10 ! 30 @ 20;
U = (10 ! 20) + 30;
X = 10 ! (30 @ 20);

/********************************************************************/

/* Sample lab4.out */

 Symbol Table 
Symbol   Value 
  B        12 
  M        20 
  P        30 
  Q        32 
  R        30 
  S        10
  T        20
  U        40
  X        10

/********************************************************************/

- Note that there is no error checking.
- The input data will follow the exact format specified in Sample
  Input, and your output must follow the exact format specified in
  Sample Output.

/********************************************************************/

What To Turn In
---------------
   - A disk containing lab4.y, lab4.l, executable code, and other
     relevant files (if any).
   - A hard copy of lab4.y and lab4.l.
   - One week before the lab is due, I will put the input on the
     course web site.  Download the input file and run your program
     with this input to generate an output file.  Turn in a hard copy
     of this output file as well.
   - Put all these in an envelope; they will be returned to you in
     the envelope.  Please use a large envelope so that you don't
     have to fold your printouts.

/********************************************************************/