/*scanner.c - lexical scanner for arithmetic expressions*/

#include "scanner.h"

/*WHICH STANDARD HEADER FILES DO YOU NEED TO INCLUDE HERE?*/

static char current_char;		/*next character to be scanned*/
Token token;				/*the token most recently scanned*/
int number;				/*if token==NumberToken, here's the #*/

static char next_char()			/*all input comes through here*/
  {
  current_char = getchar();
  }

/*sets the token type and gets the next character*/
static void make_token(t)
Token t;
  {
  next_char();
  token = t;
  }

/*On entry, 'current_char' is a digit.  Set the global variable 'number' to
  the integer represented by the string of digits, and set the global
  variable 'token' to NumberToken.*/
static void string_to_number()
  {
  token = NumberToken;
  number = 0;
/*invariant: The portion of the digit string that is to the left of the
  position of 'current_char' is the base-ten representation of 'number'.
  (For ease of specification, define the null string as a valid base-ten
  representation of the integer 0.)*/
/*In other, less declarative words, 'number' is accumulating the
  digits by place value.*/
/*bound: the number of digits that remain to be processed*/
  do
    {

/*FILL IN THE GUARD AND THE BODY OF THIS LOOP*/

    } while(		);
  }

/*initialise the scanner by loading the first character*/
void init_scanner()
  {
  next_char();
  }

/*top-level scanner function*/
void next_token()
  {

/*THERE ARE FOUR THINGS TO DO HERE:
 * FIRST, SKIP WHITE SPACE -USE THE isspace() FUNCTION FROM <ctype.h> -THEN...
 * IF THE CURRENT CHARACTER IS A DIGIT (USE isdigit()), CALL string_to_number()
 * IF THE CURRENT CHARACTER IS ONE OF +,-,*,/, or ., CALL make_token() WITH
 *    THE APPROPRIATE TOKEN (LISTED IN scanner.h)
 * IF THE CURRENT CHARACTER IS NONE OF THE ABOVE, PRINT AN ERROR MESSAGE AND
 *    END THE PROGRAM
 *YOU'LL NEED TO USE A COMBINATION OF if...else AND switch*/

  }

/*print the type and value of the token - useful in debugging*/
void print_token(t)
Token t;
  {
  switch(t)
    {
    case NumberToken: printf("%d", number); break;
    case PlusToken: putchar('+'); break;
    case MinusToken: putchar('-'); break;
    case TimesToken: putchar('*'); break;
    case DivideToken: putchar('/'); break;
    case LeftParenToken: putchar('('); break;
    case RightParenToken: putchar(')'); break;
    case PeriodToken: putchar('.'); break;
    default: printf("undefined token %d", (int)t);
    }
  }

/*ONCE YOU'RE DONE WITH THIS PROGRAM, GET scanner.h AND testscan.c, AND
  COMPILE THEM AND LINK THEM ALL TOGETHER LIKE THIS:
  cc -g -o testscan testscan.c scanner.c
*/