After:

// Compute the tax on a purchase
int main()
{
   // Symbolic constants
   const double NY_RATE = 0.06875;
   const double NJ_RATE = 0.065;

   // Variable declarations
   double cost, tax;
   char state;

   // Input the cost of purchase
   cout << "Enter the cost of purchase" << endl;
   cin >> cost;

   // Input the state where purchased
   cout << "Enter the state where purchased: 'y' for New York and 'j' for New Jersey" << endl;
   cin >> state;   

   // Compute the tax on the purchase
   if( 'y' == state )
      tax = cost * NY_RATE;
   else
      tax = cost * NJ_RATE;

   // Print the tax on the purchase
   cout << "The tax on purchase of $ " << cost 
        << " is " << tax << endl;

   return 0;
}