#include <stdio.h>

double square(double x); 

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

   a = 4;

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

   printf( "Square of %lf = %lf\n", a, b);
}

double square( double x )                  
{
   double r;           // Define a local variable         

   r = x * x;       // Statement

   return ( r );    // Return statement
}