A Simple Grammar

/* (c) Roman "Krishna" Bystritsky, 2001 */
/* file agram.cpp */
#include "string.hpp"
#include "iostream.h"
#include "stdio.h"
#include "agram.h"
/*
 * Grammar:
 *
 *	<formula> -> <term> { +/- <term> }
 * <term>	 -> <element> { *\'/' <element> }
 *	<element> -> ( <formla> ) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0
 *	+/-	  ->	+		|	-
 * * \ '/' -> *		| /	
**/
/*	<formula> -> <term> { +/- <term> } */
int	parseFormula( String& in, String& out, int& infix)
{
	char	cSign;
	if(parseTerm(in,out, infix))
 {
 	cout << "From parseFormula"<<endl;
  return RET_ERR;
 }
 while( IsPM(cSign=in[infix]) )
 {
 	infix++;
  if(parseTerm(in,out,infix))
  {
	 	cout << "From parseFormula"<<endl;
 	 return RET_ERR;
  } 
  out += cSign;
  out += ' ';
 }
 return RET_OK;
}
/* <term>	 -> <element> { *\'/' <element> } */
int	parseTerm(String& in, String& out, int& infix)
{
	char	cSign;
	if(parseElem(in,out,infix))
 {
 	cout << "From parseTerm" << endl;
  return RET_ERR;
 }
 while( IsMD(cSign=in[infix]) )
 {
 	infix++;
  if(parseElem(in,out,infix))
  {
	 	cout << "From parseTerm"<<endl;
 	 return RET_ERR;
  } 
  out += cSign;
  out += ' ';
 }
	return RET_OK;
}
/*	<element> -> ( <formla> ) | digit+*/
int	parseElem(String& in, String& out, int& infix)
{
	char cSign;
	cSign = in[infix];
	if(IsOB(cSign))	// case of ( formula )
 {
  infix ++;
 	if(parseFormula(in,out, infix))
  {
  	cout << "from parseElem" << endl;
   return RET_ERR;
  }
  cSign = in[infix];
  infix++;
  if(!IsCB(cSign))
  {
  	cout << "parseElem: missing close brace c. " << infix+1 <<" "<<endl;
   return RET_ERR;
  }
 } else 
 {
 	while(IsDigit(cSign))
  {
  	out += cSign;
   cSign= in[++infix];
  }
  if(cSign == '.' || cSign== ',')
  {
   out+='.';
  	cSign=in[++infix];
	 	while(IsDigit(cSign))
	  {
	  	out += cSign;
	   cSign= in[++infix];
	  }
  }
  out += ' ';
 }
 return RET_OK;
}
int parseExpression(String& in, String& out)
{
 int		infix = 0;
 if(parseFormula(in, out, infix))
 {
 	cout << "from parseExpression" << endl;
  return RET_ERR;
 }
 if(infix != in.length())
 {
 	cout << "parseExpression: Unknown symbol c. " << infix +1 << endl;
  return RET_ERR;
 }
 return RET_OK;
}