#include <stdio.h>

/* In this example, we do not declare function before we define it
   because function's definition appears before main() is defined.  */

/* Note that a separate type should be specified for each parameter 
   of the function, even if all parameters have the same type.
*/
double average(double a, double b)
{
double res;
/* variable  res  declared within this function is local to this function.
It cannot be accessed or modifed by any other function 
*/
	res = (a + b)/ 2.0 ;

return( res );
}


int main( void )
{
double x,y,z, avg;

	printf("Enter 3 floating point numbers\n");
	scanf("%lf %lf %lf", &x, &y, &z);
	
  /* We demonstrate how can we call an external function average(a,b). Since
     this function returns a value, the produced value can be stored in a
     variable, printed, used in an arithmetical expression or used as an argument.
   */
	
  printf("Example 1: average of 10.0 and 20.0 = %lf\n", average(10.0, 20.0) );

  /* The return value from average(a,b) function is not captured anywhere. 
     If we need it later in our program, we can keep it in a variable.
     In the following example, we call function average a few times, use 
     return values to do some computation and save result in the variable avg.
   */
  
  avg = (average(x,y) + average(y,z) + average(x,z))/3.0 ;
  
  printf("Example 2: avg = %lf\n", avg);
	
  printf("Example 3: compute average of x*x and y/2 = %lf\n", average(x*x,y/2.0) );
  
  printf("Example 4: nested average = %lf\n", average(average(x,y), average(y,z)) );

return(0);
}