#include <stdio.h>


int main( int argc, char *argv[] )
{
   double a, b;

   a = 4.0;

   b = square( a );  // Call function square

   extern double square( double x ) ;   // Too late !!!
   extern void print ( double x ) ;

   print( a );       // Call function print
   print( b );       // Call function print                  
}