// EX4_01.CPP
  // Calculating gas mileage
  include <iostream>
  include <iomanip>
  
  using std::cin;
  using std::cout;
  using std::endl;
  using std::setw;
  
  int main()
  {
     const int MAX = 20;                     // Maximum number of values
     double gas[ MAX ];                      // Gas quantity in gallons
     long miles[ MAX ];                      // Odometer readings
     int count = 0;                          // Loop counter
     char indicator = 'y';                   // Input indicator
  
     while( (indicator == 'y' || indicator == 'Y') && count < MAX ) 
     {
        cout << endl
             << "Enter gas quantity: ";
        cin >> gas[count];                   // Read gas quantity
        cout << "Enter odometer reading: ";
        cin >> miles[count];                 // Read odometer value
  
        ++count;
        cout << "Do you want to enter another(y or n)? ";
        cin >> indicator;      
     }
  
     if(count <= 1)                     // count = 1 after 1 entry completed
     {                                  // ... we need at least 2
        cout << endl
             << "Sorry - at least two readings are necessary.";
        return 0;
     }
  
     // Output results from 2nd entry to last entry
     for(int i = 1; i < count; i++)            
     cout << endl
          << setw(2) << i << "."             // Output sequence number
          << "Gas purchased = " << gas[i] << " gallons" // Output gas
          << " resulted in "                 // Output miles per gallon
          << (miles[i] - miles[i - 1])/gas[i] << " miles per gallon.";
  
     cout << endl;
     return 0;
  }