// testing multiple functions at two points
//  using a table and pointer
//  and function pointer arguments to a function
//
#include <stdio.h>
#include <math.h>

double my_sqrt( double x) { return exp(log(x)/2); }
double my_cbrt( double x) { return exp(log(x)/3); }
double my_atan( double x) { return atan2(x,1); }

typedef double (*Func)(double); // Func is type of variable

void test( const char *s, Func f, Func g, double x) {
  double y1 = f(x); // or: (*f)(x)
  double y2 = g(x);
  printf( "%s %g %g %g\n", s, x, y1, y2);
}

struct list { 
  char *s; Func f, g; double x[2];
}
table[] = {
 { "sqrt", my_sqrt, sqrt, { 2, 10} }, 
 { "cbrt", my_cbrt, cbrt, { 2, 10} }, 
 { "atan", my_atan, atan, { 1, 23} }, 
 {      0,       0,    0, { 0 }    }
};

int main( void)
{
  for( struct list *p = table; p->s != 0; ++p) {
   for( int i = 0; i < 2; ++i) {
     test( p->s, p->f, p->g, p->x[i]);
   }
  }

}

/* output:

sqrt 2 1.41421 1.41421
sqrt 10 3.16228 3.16228
cbrt 2 1.25992 1.25992
cbrt 10 2.15443 2.15443
atan 1 0.785398 0.785398
atan 23 1.52735 1.52735

*/