/* This program is a recursive descent parser. */

#include<ctype.h>
#include<stdlib.h>
#include<stdio.h>
#include<iostream.h>

int token;

void end_of_line();
int expression();
int term();
int factor();
int number();
int digit();

void error()
{
  cerr << "parse error" << endl;
  exit(1);
}

void getToken()
{ 
  scanf("%c", &token);
  //token = getchar();
}

void match(char c)
{ if(token == c) 
    getToken();
 else
   error();
}

void end_of_line()
{ int result = expression();
 if(token == '\n')
    cout <<"The result is: " << result << endl;
 else
  error();
}

int expression()
{ int result = term();
 while (token == '+')
   { match('+');
     result += term();
   }
 return result;
}

int term()
{ int result = factor();
 while(token == '*')
   { match('*');
     result *= factor();
   }
 return result;
}

int factor()
{ int result;
 if(token =='(')
   { match('(');
     result = expression();
     match(')');
   }
 else
   result = number();
 return result;
}

int number()
{ int result = digit();
 while(isdigit(token))
   result = 10 * result+ digit();
 return result;
}

int digit()
{ int result;
 if(isdigit(token))
   { result = token - '0';  // convert to a number
   match(token);
   }
 else
   error();
 return result;
}

void parse_it()
{ cout << "Input an arithmetic expression, use positive integers," << endl; 
  cout << "zero, '(', ')', '+', and '*' " << endl;
  getToken();
  end_of_line();
}

main() 
{ parse_it();
 return 0;
}