// testing multiple functions at two points
//  using a table and array indexing
//
#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

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

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

*/