lex.c

#include "lex.h"
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>


char* yytext = ""; /* Lexeme (not '\0'
                      terminated)              */
int yyleng   = 0;  /* Lexeme length.           */
int yylineno = 0;  /* Input line number        */
  

int lex(void){

   static char input_buffer[1024];
   char        *current;
   int first_char_is_digit = 0;
   int invalid_num= 0;

   current = yytext + yyleng; /* Skip current
                                 lexeme        */

   while(1){       /* Get the next one         */
      while(!*current ){
         /* Get new lines, skipping any leading
         * white space on the line,
         * until a nonblank line is found.
         */

         
         if(!gets(input_buffer)){
            *current = '\0' ;

            return EOI;
         }
         current = input_buffer;
         ++yylineno;
         while(isspace(*current))
            ++current;
      }
  //    printf("%s\n", current);
      for(; *current; ++current){
         /* Get the next token */
         yytext = current;
         yyleng = 1;
         switch( *current ){
           case ':':
        //    printf("ASSIGN\n");
            return ASSIGN;
           case '=':
         //   printf("EQUALS\n");
           return EQUALS;
           case '<':
         //   printf("LT\n");
              return LT;
            return LT;
           case '>':
         //   printf("GT\n");
            return GT;
           case ';':
         //   printf("semi colon\n");
            return SEMI;
           case '+':
         //  printf("plus\n");
            return PLUS;
           case '-':
         //  printf("minus\n");
            return MINUS;
           case '*':
         //  printf("mul\n");
            return TIMES;
           case '/':
         //  printf("div\n");
            return DIV;
           case '(':
         //   printf("lp\n");
            return LP;
           case ')':
         //   printf("rp\n");
            return RP;
           case '\n':
           case '\t':
           case ' ' :
            break;
           default:
            if(!isalnum(*current))
               fprintf(stderr, "Agvonse la8emevn eisagwgn <%c>\n", *current);
            else{               

               if(isdigit(*current)) 
                  first_char_is_digit = 1;
               
                current++;
               while(isalnum(*current)){
                  if(isalpha(*current)){

                    if(first_char_is_digit && !invalid_num)
                        invalid_num = 1;
                  }

                  
                  ++current;
               }

               yyleng = current - yytext;
               if(invalid_num)
                  fprintf(stderr, "Neither number nor id\n");
               else
                  if(first_char_is_digit)
                      return NUM;
                  else
                      return find_keyword();
            }
            break;
         }
      }
   }
}


static int Lookahead = -1; /* Lookahead token  */

int match(int token){
   /* Return true if "token" matches the
      current lookahead symbol.                */

   if(Lookahead == -1)
      Lookahead = lex();

   return token == Lookahead;
}

void advance(void){
/* Advance the lookahead to the next
   input symbol.                               */

    Lookahead = lex();
//    printf("%d\n", Lookahead);
}

int find_keyword(){
  char *temp;
  int i;
  temp = (char *) malloc(sizeof(char) * (yyleng+1));
  temp[yyleng]='\0';
  for(i=0;i<yyleng;i++){
    temp[i]=yytext[i];
  }
  
  /*Compare for keywords*/
  if(!strcmp(temp,"if")){
    return IF;
  }
  else if(!strcmp(temp,"then")){
    return THEN;
  }
  else if(!strcmp(temp,"while")){
    return WHILE;
  }
  else if(!strcmp(temp,"do")){
    return DO;
  }
  else if(!strcmp(temp,"begin")){
    return BEGIN;
  }
  else if(!strcmp(temp,"end")){
    return END;
  }
  else{
    return ID;
  }
}