// Practical Lab Assignment-7(Week 9)
// ID:U1910049 Name: Rustam Zokirov
// Program to calculate area of a circle using functions

#include <iostream>
#include <math.h> //C++ libriry which is including "pow" and PI=3.14
using namespace std;

float area(float radius)
{ // function for calculating the area
	float area;
	area = (atan(1) * 4) * (pow(radius, 2)); //"atan" is the function which is finding the PI=3.14
	return area;
} // end function "area"

int main1()
{
	float radius;
	cout << "Please enter the radius of circle: ";
	cin >> radius; // inputing the radius

	if (radius > 0)
		cout << area(radius) << endl; // calling the function "area" for calculating the Area of Circle

	else
		cout << "INVALID Radius!" << endl; // if radius is a negative number or equal to zero the program will show "Invalid radius"
	system("pause");
	return 0;
}