#include <stdio.h>

char nextChar;   /* next character read from input */
int charClass;

/* character classes: */
#define LETTER    0      /* [a-zA-Z] */
#define DIGIT     1      /* [0-9] */
#define UNKNOWN   2      /* .*   */
#define SLASH     3
#define STAR      4
#define HYPHEN    5
/* also EOF from stdio.h */

/* tokens: */
#define GENERIC_TOKEN        1
#define INTEGER_LITERAL      2
#define UNKNOWN_TOKEN        3
#define INT_DATA_TYPE_TOKEN  4
#define SLASH_OPERATOR       5
#define COMMENT              6
#define MINUS_OPERATOR       7

#define MAXLENGTH 80
char lexeme[MAXLENGTH];
int lexemeLength;

/* getChar() function */
void getChar()
{
  /* get next character from stdin */
  nextChar = getc(stdin);

  /* determine the character class */
  if (nextChar == EOF)
    charClass = EOF;
  else if (nextChar == '/')
    charClass = SLASH;
  else if (nextChar == '*')
    charClass = STAR;
  else if (nextChar == '-')
    charClass = HYPHEN;
  else if (isalpha(nextChar))
    charClass = LETTER;
  else if (isdigit(nextChar))
    charClass = DIGIT;
  else
    charClass = UNKNOWN;
}

/* addChar() function */
void addChar()
{
  if (lexemeLength < MAXLENGTH) {
    lexeme[lexemeLength++] = nextChar;
    lexeme[lexemeLength] = '\0';
  } else
    fprintf(stderr, "ERROR: Lexeme is too long\n");
}


/* lookup() function */
int lookup(char *lexeme)
{
  if ( strcmp( lexeme, "int" ) == 0 )
    return INT_DATA_TYPE_TOKEN;
  else
    return GENERIC_TOKEN;
}


int lex()
{
  lexemeLength = 0;
  static int first = 1;

  if (first) {
    getChar();
    first = 0;
  }

  /* skip whitespace */
/*  while (isspace(nextChar))
    getChar();   */

  switch (charClass)
  {
    case LETTER:
      addChar();  getChar();
      while ( charClass == LETTER || charClass == DIGIT ) {
        addChar();  getChar();
      }
      return lookup(lexeme);

    case HYPHEN:
    case DIGIT:
     {
      int isNegative = (charClass == HYPHEN);
      addChar();  getChar();

      if (isNegative && charClass != DIGIT)
        return MINUS_OPERATOR;

      while (charClass == DIGIT) {
        addChar();  getChar();
      }
      return INTEGER_LITERAL;
     }

    case SLASH:
      addChar();  getChar();
      if (charClass == STAR)
      {
        int comment_done = 0;
        while (!comment_done)
        {
          addChar();  getChar();
          while (charClass == STAR) {
            addChar();  getChar();
            if (charClass == SLASH) {
              addChar();  getChar();
              comment_done = 1;
            }
          }
        }
        return COMMENT;
      } else
        return SLASH_OPERATOR;

    case UNKNOWN:
    case STAR:
      addChar();  getChar();
      return UNKNOWN_TOKEN;

    case EOF:
      return EOF;
  }
}


main()
{
  int x;

  int y = -5;
  int q = 5-y;
  int r = q-5;
  int s = q - -5;

  do
  {
    x = lex();

    if (x != COMMENT)
    {
      if (x == INTEGER_LITERAL)
        printf("[INTEGER_LITERAL] ");
      else if (x == MINUS_OPERATOR)
        printf("[MINUS_OPERATOR] ");

      printf("%s", lexeme);
    }

  } while (x != EOF);

}