# Circumference and circular area

The user is first prompted to enter a radius. Then the circumference and area of the circle are calculated, rounded and output to the screen.

## Code Example

``````import java.util.Scanner;

class CircumferenceCircularArea {
public static void main(String[] args) {
double r, area, circumference;

// calculation of circumference
circumference = 2 * Math.PI * r;

// calculation of circular area
// Math.pow(base, exponent): Returns base raised to the power exponent
area = Math.PI * Math.pow(r, 2);

System.out.println("Circumference: " + String.format("%1.2f", circumference));
System.out.println( "Circular Area: " + String.format("%1.2f", area));
}
}``````
##### Output
``````Please enter radius: 4.5
Circumference: 28.27
Circular Area: 63.62``````

### Code Explanation

`import java.util.Scanner;` imports the `Scanner` class from the `java.util` package. This class is used to read user input from the console.

`class CircumferenceCircularArea` declares a class named `CircumferenceCircularArea`.

`public static void main(String[] args)` is the main method of the program where the execution starts. It takes an array of strings as a parameter (although it is not used in this program).

The following lines declare variables:

``````Scanner reader = new Scanner(System.in);
double r, area, circumference;``````

Here, `reader` is an instance of the `Scanner` class that is used to read user input. `r` is a double variable to store the radius entered by the user, and `area` and `circumference` are double variables to store the calculated values.

`System.out.print("Please enter radius: ");` displays a prompt message asking the user to enter the radius.

`r = reader.nextDouble();` reads a double value entered by the user using the `nextDouble()` method of the `Scanner` class. The value entered by the user is stored in the `r` variable.

`reader.close();` closes the `Scanner` object to release system resources after reading the user input.

`circumference = 2 * Math.PI * r;` calculates the circumference of the circle using the formula `2 * π * r`, where `Math.PI` represents the mathematical constant π.

`area = Math.PI * Math.pow(r, 2);` calculates the circular area using the formula `π * r^2`. The `Math.pow(base, exponent)` function is used to raise `r` to the power of 2.

The following lines print the calculated values:

``````System.out.println("Circumference: " + String.format("%1.2f", circumference));
System.out.println("Circular Area: " + String.format("%1.2f", area));``````

The `System.out.println()` statements display the calculated circumference and circular area values. The `String.format("%1.2f", value)` is used to format the double values with two decimal places before displaying them.