// testing two functions at two points
//  using separate arrays
//
#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); }

typedef double (*Func)(double); // Func is type of variable, pointer to function

int main( void)
{
  double x[2] = { 2, 10};
  Func f[2] = { my_sqrt, my_cbrt };
  Func g[2] = { sqrt, cbrt };
  char *s[2] = { "sqrt", "cbrt" };

  for( int j = 0; j < 2; ++j) {
   for( int i = 0; i < 2; ++i) {
     double y1 = f[j](x[i]);
     double y2 = g[j](x[i]);
     printf( "%s %g %g %g\n", s[j], x[i], y1, y2);
   }
  }

}

/* 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

*/