Binary Search:

2 6 15 42 55 89 111 256

2 =  10

6 = 110

15 = 1111

42 = 101010

55 = 110111

89 = 1011001

111 = 1101111

256 = 100000000

#include <iostream>

const double PI = 3.14159;

int main() {

   double diameter;

   std::cin >> "Please enter the diameter of the circle:" << std::endl;

   std::cin >> diameter;

   double radius = diameter / 2;

   double area = radius * radius * PI;

   double circumference = 2 * radius * PI; // or diameter * PI;

   std::cout << "Area: " << area << std::endl;

   std::cout << "Circumference: " << circumference << std::endl;

}

Explanation:

The first line imports the read/write library. The rest should be self-explanatory.