[Dev-C++] delete statement gives segmentation fault error

[Dawood V. <da...@ku...>]

Hello every body,
	below is a straight code from Stroustrup's classic.  I am running 
bloodshed DEV-C++. At the end, it is trying to delete the object "input" 
using delete statement.  It straightaway gives me invalid memory or 
segmentation fault error.  Also, if I comment the delete statement, the 
code works fine as it should be.  Actually it happens, only when I try to 
pass the command line arguement. As u all know, it is the famous calculator 
example from the 6th chapter of the book.  Right now, I am in the 6th 
chapter, so I do not have a very good idea about new and delete 
statements.  According to me the code should work, as we are trying to 
delete the object we explicitly created.

#include <iostream>
#include <string>
#include <map>
#include <cctype>
#include <strstream>

enum Token_value{
       NAME, NUMBER,END,
       PLUS = '+',MINUS = '-', MUL = '*', DIV = '/',
       PRINT = ';', ASSIGN = '=', LP = '(', RP = ')'
};

Token_value curr_tok  = PRINT;

double number_value;
string string_value;
istream* input;


int no_of_errors;
double error(const string& s) {
   no_of_errors++;
   cerr<<"error: "<<s<<'\n';
   return 1;
}

Token_value get_token() {
   char ch;
   do { // skip whitespace except \n
       if (!((*input).get(ch))) return curr_tok = END;
   } while (ch!= '\n' && isspace(ch));

   switch (ch) {
   case ';':
   case '\n':
     return curr_tok = PRINT;
   case '*':
   case '/':
   case '+':
   case '-':
   case '(':
   case ')':
   case '=':
     return curr_tok = Token_value(ch);

   case '0':
   case '1':
   case '2':
   case '3':
   case '4':
   case '5':
   case '6':
   case '7':
   case '8':
   case '9':
   case '.':
     (*input).putback(ch);
     (*input)>> number_value;
     return curr_tok = NUMBER;
   default:
     if (isalpha(ch)) {
       string_value = ch;
       while ((*input).get(ch) && isalnum(ch))
          string_value+=ch;
       (*input).putback(ch);
       return curr_tok = NAME;
     }
     error ("bad token");
     return curr_tok = PRINT;
   }
}

//------------------------------------------------ prim(bool get)
double expr(bool);
map<string,double>table;

double prim(bool get) {   // handle primaries
   if (get) get_token();

   switch(curr_tok){
   case NUMBER:       //floating point constant
   {
     double v = number_value;
     get_token();
     return v;
   }
   case NAME:
   {
     double& v = table[string_value];
     if (get_token() == ASSIGN)
       v = expr(true);
     return v;
   }
   case MINUS:  // unary minus
     cout<<"reading negative number\n";
     return  -prim(true);
   case LP:
   {
     double  e =  expr(true);
     if (curr_tok != RP) return error("')' expected");
     get_token();  //eat ')'
     return e;
   }
   default:
     return error ("primary expected");
   }
}

//------------------------------------------------ term(bool get)
double term(bool get){          // multiply and divide
   double left = prim(get);

   for (;;)
     switch (curr_tok) {
     case MUL:
       left *= prim(true);
       break;
     case DIV:
       if (double d = prim(true)) {
         left /= d;
         break;
       }
       return error("divide by zero");
     default:
       return left;
     }
}

//------------------------------------------------ expr(bool get)
double expr(bool get) {      // add and subtract
   double left = term(get);

   for(;;)                     //forever
     switch (curr_tok) {
     case PLUS:
       left += term(true);
       break;
     case MINUS:
       left -= term(true);
       break;
     default:
       return left;
   }
}


int main(int argc, char* argv[])
{
   argv[0] = "dc";
   argv[1] = "rate = 2.5; distance = rate * 5;";
   argc = 2;
   switch (argc) {
     case 1:
       input = &cin  ;
       break;
     case 2:
       input = new istrstream(argv[1]);
       break;
     default:
       error("too many arguements");
       return 1;
   }
   table ["pi"] = 3.1415926535897932385;
   table ["e"] = 2.718281828459042354;

   while (*input) {
     get_token();
     if (curr_tok == END) break;
     if (curr_tok == PRINT) continue;
     cout << expr(false) << '\n';
   }

   if (input != cin) delete input;
   return no_of_errors;

       system("PAUSE");
       return 0;
}