#include <stdio.h>
#include <math.h>

double log_two(double x){
  return 1.0 / log(2.0) * log(x);
}

int main(void) {

  double radius = 4.0, d;
  int i;

  printf("Area of circle = %f\n", radius * radius * 3.14159);
  printf("Circumference of circle =  %f\n", 2 * radius * 3.14159);

  printf("log(e) = %f\n", log(2.71828));
  printf("log10(e) = %f\n", log10(2.71828));
  printf("log2(e) = %f\n\n", log_two(2.71828));

  printf("%d examples with log2:\n", 5);
  for (i = 1, d = 2.0; i <= 5; i++, d *= 2)
    printf("log2(%f) = %f\n", d, 1.0 / log(2.0) * log(d));

  return 0;
}