697: Mainline

Suspending disbelief, suppose that you decide to “improve” the rabbits program by dividing it into three files, one for each of the three key functions. One file, rabbits.cxx, contains main and rabbits:

//  The rabbits.cxx file 
#include  
// Space reserved to include files 
int rabbits (int n) { 
  if (n == 0 || n == 1) 
     return 1; 
   else return previous_month (n) + penultimate_month (n);} 
main ( ) { 
  int months; 
  cout << "Please supply the number of months. 
       << endl; 
  cin >> months; 
  cout << "After " 
       << months << " months, there are " 
       << rabbits(months) << "rabbits."  
       << endl; 
} 

The other files, previous.cxx and penultimate.cxx are simpler:

// The previous.cxx file 
// Space reserved to include files 
int previous_month (int n) {return rabbits ((n - 1));} 
  
// The penultimate.cxx file 
// Space reserved to include files 
int penultimate_month (int n) {return rabbits ((n - 2));}