// Step 1: Include necessary header files
#include <iostream>
// Step 2: Define a constant using #define
#define PI 3.14159
// Step 3: Main function
int main() {
// Step 4: Declare variables
double radius, area;
// Step 5: Prompt user for input
std::cout << "Enter the radius of a circle: ";
// Step 6: Read user input
std::cin >> radius;
// Step 7: Calculate area using the defined constant
area = PI radius radius;
// Step 8: Display the result
std::cout << "The area of the circle is: " << area << std::endl;
// Step 9: Return 0 to indicate successful completion
return 0;
}