READTOKN.c

/*----- FILE READTOKN.C ----------------------------------------------*/
/*                                                                    */
/* A function to read input and tokenize it for a simple calculator   */
/*--------------------------------------------------------------------*/
#include <ctype.h>
#include <stdio.h>
#include "CALC.h" //<----- we replaced ‘ #include "calc.h"  ’ by ‘ #include "CALC.h"  ’
/*--------------------------------------------------------------------*/
/* action: get next input char, update index for next call            */
/* return: next input char                                            */
/*--------------------------------------------------------------------*/
static char nextchar(void)
{
/*--------------------------------------------------------------------*/
/* input  action:                                                     */
/*    2      push 2 on stack                                          */
/*    18     push 18                                                  */
/*    +      pop 2, pop 18, add, push result (20)                     */
/*    =      output value on the top of the stack (20)                */
/*    5      push 5                                                   */
/*    /      pop 5, pop 20, divide, push result (4)                   */
/*    =      output value on the top of the stack (4)                 */
/*--------------------------------------------------------------------*/
  char * buf_in  = "2 18 + = 5 / = ";
  static int index;     /* starts at 0 */
  char ret;
  ret = buf_in[index];
  ++index;
  return ret;
}
/*--------------------------------------------------------------------*/
/* output: buf - null terminated token                                */
/* return: token type                                                 */
/* action: reads chars through nextchar() and tokenizes them          */
/*--------------------------------------------------------------------*/
Token read_token(char buf[])
{
  int i;
  char c;
  /* skip leading white space */
  for( c=nextchar();
       isspace(c);
       c=nextchar())
    ;
  buf[0] = c;  /* get ready to return single char e.g."+" */
  buf[1] = 0;
  switch(c)
  {
    case '+' : return T_PLUS;
    case '-' : return T_MINUS;
    case '*' : return T_TIMES;
    case '/' : return T_DIVIDE;
    case '=' : return T_EQUALS;
    default:
      i = 0;
      while (isdigit(c)) {
        buf[i++] = c;
        c = nextchar();
      }
      buf[i] = 0;
      if (i==0)
        return T_STOP;
      else
        return T_INTEGER;
  }
}