Answer:
#include <iostream>
const double PI = 3.14159;
int main() {
double diameter;
std::cout << "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.
std::cin is the input stream - we use it to get the diameter
std::cout is the output stream - we write the answers (and commentary) there.
std::endl is the special "character" informing the output stream that we want it to put a newline character (and actually print to the output - it might have been holding off on it).
the // in the circumference computation signifies a comment - the program simply ignores this. I've added it to tell the reader that the circumference could have been computed using the diameter,
