/*
A -> I = E
E -> T + E | T - E | T
T -> P * T | P / T | P
P -> I | L | (E)
I -> a | b | ... | y | z
L -> 0 | 1 | ... | 8 | 9
*/
 
#include <iostream>
#include <fstream>
#include <string>
 
using namespace std;
 
 
bool literal(char *);
bool integer(char *);
bool primary(char *);
bool term(char *);
bool expr(char *);
bool assign(char *);
 
int main ()
{
    ifstream inFile;
    inFile.open("experiment.txt");
 
    string line;
    inFile >> line;
 
 
    char *c;
    c = &line[0];
 
    cout << "String read from file: " << line << endl;
 
 
    if (assign(c))
       cout << "The string: '" << line << "' is in the language" << endl;
    else
       cout << "The string: '" << line << "' is not in the language" << endl;
 
 
 
 system("Pause");
    return 0;
}
bool assign (char *c)
{
    if (integer(c))
    {        
 
         ++c;  
         if (*c == '=')
         {             
             ++c;              
             if (expr(c))
             {                
                ++c; 
                return true;       
             }
         }
     }
     else
         return false;
}
 
bool literal(char *c)
{
     if (*c == 0 || *c == 1 || *c == 2 || *c == 3 || *c == 4 || *c == 5 || *c == 6 || *c == 7 || *c == 8 || *c == 9)
     {   
 
        return true;
     }
     return false;
}
 
bool integer (char *c)
{
     cout << "in integer" << endl;
     if (*c == 'a' || *c == 'b' || *c == 'c' || *c == 'd' || *c == 'e' || *c == 'f' || *c == 'g' || *c == 'h' || *c == 'i' || *c == 'j' || *c == 'k' || *c == 'l' || *c == 'm' || *c == 'n' || *c == 'o' || *c == 'p' || *c == 'q' || *c == 'r' || *c == 's' || *c == 't' || *c == 'u' || *c == 'v' || *c == 'w' || *c == 'x' || *c == 'y' || *c == 'z')
     {
        return true;
     }
     else
         return false;
}
 
bool primary (char *c)
{
     if(integer(c))
        return true;
     else if (literal(c))
          return true;
     else if (*c == '(')
          ++c;
          if (expr(c))
          {
             ++c;
             if (*c == ')')
             {
                ++c;
                return true;
             }
             else
                 return false;
          }
          else
              return false;
}
 
bool term (char *c)
{
     if (primary(c))
     {
          ++c;
          if (*c == '*' || *c == '/')
          {
             ++c;
             if (term(c))
             {
                return true;
             }
             else
                 return false;
          }
          return true;
     }
     else
         return false;
}
 
bool expr (char *c)
{
     if (term(c))
     {
          ++c;          
          if (*c == '+' || *c == '-')
          {
             ++c;
             if (expr(c))
             {                
                return true;
             }
          }
          return true;
     }
     else
         return false;
}